From 43a97878ce14b72f0981164f87f2e35e14151312 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Sun, 7 Apr 2024 11:22:09 +0200
Subject: Adding upstream version 110.0.1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 .../css/animation-duration-auto.tentative.html     |  56 ++
 .../scroll-animations/css/animation-shorthand.html |  43 ++
 .../css/animation-timeline-computed.html           |  76 ++
 .../css/animation-timeline-ignored.tentative.html  | 145 ++++
 .../css/animation-timeline-in-keyframe.html        |  27 +
 .../css/animation-timeline-multiple.html           |  90 +++
 ...e-named-scroll-progress-timeline.tentative.html | 662 ++++++++++++++++++
 .../css/animation-timeline-none.html               |  41 ++
 .../css/animation-timeline-parsing.html            |  88 +++
 ...eline-scroll-functional-notation.tentative.html | 148 ++++
 ...imeline-view-functional-notation.tentative.html | 263 +++++++
 .../css/get-animations-inactive-timeline.html      |  87 +++
 ...keyframes-with-document-timeline.tentative.html |  54 ++
 ...imeline-none-with-progress-print.tentative.html |  56 ++
 .../animation-timeline-none-with-progress-ref.html |  38 +
 .../scroll-timeline-default-iframe-print.html      |  65 ++
 .../scroll-timeline-default-print.tentative.html   |  62 ++
 .../scroll-timeline-specified-scroller-print.html  |  58 ++
 .../scroll-timeline-specified-scroller-ref.html    |  38 +
 ...on-animation-longhand-properties.tentative.html | 255 +++++++
 .../css/progress-based-animation-timeline.html     |  52 ++
 .../scroll-timeline-axis-computed.tentative.html   |  35 +
 .../scroll-timeline-axis-parsing.tentative.html    |  27 +
 .../css/scroll-timeline-axis-writing-mode.html     | 126 ++++
 .../css/scroll-timeline-default-iframe-ref.html    |  33 +
 .../css/scroll-timeline-default-iframe.html        |  73 ++
 .../css/scroll-timeline-default-quirks-mode.html   |  63 ++
 .../css/scroll-timeline-default-ref.html           |  31 +
 ...croll-timeline-default-writing-mode-rl-ref.html |  32 +
 .../scroll-timeline-default-writing-mode-rl.html   |  65 ++
 .../css/scroll-timeline-default.html               |  63 ++
 .../scroll-timeline-document-scroller-quirks.html  |  36 +
 .../css/scroll-timeline-dynamic.tentative.html     | 267 +++++++
 .../scroll-timeline-frame-size-changed-ref.html    |  31 +
 .../css/scroll-timeline-frame-size-changed.html    |  67 ++
 .../css/scroll-timeline-in-container-query.html    |  74 ++
 .../css/scroll-timeline-inactive.html              |  51 ++
 .../scroll-timeline-inline-orientation-ref.html    |  32 +
 .../css/scroll-timeline-inline-orientation.html    |  68 ++
 .../css/scroll-timeline-multi-pass.tentative.html  | 109 +++
 .../scroll-timeline-name-computed.tentative.html   |  34 +
 .../scroll-timeline-name-parsing.tentative.html    |  30 +
 .../css/scroll-timeline-name-tree-scoped.html      | 144 ++++
 .../css/scroll-timeline-nearest-dirty.html         |  42 ++
 .../css/scroll-timeline-paused-animations.html     |  95 +++
 ...roll-timeline-responsiveness-from-endpoint.html |  62 ++
 .../css/scroll-timeline-root-dirty.html            |  35 +
 .../css/scroll-timeline-sampling.html              |  46 ++
 .../css/scroll-timeline-shorthand.tentative.html   |  41 ++
 .../css/scroll-timeline-sibling-gcs.html           |  52 ++
 .../scroll-animations/css/support/testcommon.js    |  19 +
 ...e-range-name-offset-in-keyframes.tentative.html |  94 +++
 .../css/view-timeline-animation.html               | 219 ++++++
 .../css/view-timeline-axis-computed.html           |  37 +
 .../css/view-timeline-axis-parsing.html            |  29 +
 .../css/view-timeline-delay-animation.html         | 144 ++++
 .../css/view-timeline-dynamic.html                 | 183 +++++
 .../css/view-timeline-inset-animation.html         | 768 +++++++++++++++++++++
 .../css/view-timeline-inset-computed.html          |  41 ++
 .../css/view-timeline-inset-parsing.html           |  34 +
 .../css/view-timeline-lookup.html                  | 301 ++++++++
 .../css/view-timeline-name-computed.html           |  36 +
 .../css/view-timeline-name-parsing.html            |  30 +
 .../css/view-timeline-name-tree-scoped.html        | 145 ++++
 .../css/view-timeline-shorthand.tentative.html     | 104 +++
 .../css/view-timeline-used-values.html             | 104 +++
 66 files changed, 6556 insertions(+)
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-duration-auto.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-shorthand.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-timeline-computed.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-timeline-ignored.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-timeline-in-keyframe.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-timeline-multiple.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-timeline-named-scroll-progress-timeline.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-timeline-none.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-timeline-parsing.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-timeline-scroll-functional-notation.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/animation-timeline-view-functional-notation.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/get-animations-inactive-timeline.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/named-range-keyframes-with-document-timeline.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/printing/animation-timeline-none-with-progress-print.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/printing/animation-timeline-none-with-progress-ref.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-default-iframe-print.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-default-print.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-specified-scroller-print.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-specified-scroller-ref.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/progress-based-animation-animation-longhand-properties.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/progress-based-animation-timeline.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-computed.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-parsing.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-writing-mode.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-iframe-ref.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-iframe.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-quirks-mode.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-ref.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-writing-mode-rl-ref.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-writing-mode-rl.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-default.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-document-scroller-quirks.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-dynamic.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-frame-size-changed-ref.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-frame-size-changed.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-in-container-query.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-inactive.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-inline-orientation-ref.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-inline-orientation.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-multi-pass.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-computed.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-parsing.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-tree-scoped.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-nearest-dirty.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-paused-animations.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-responsiveness-from-endpoint.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-root-dirty.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-sampling.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-shorthand.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/scroll-timeline-sibling-gcs.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/support/testcommon.js
 create mode 100644 testing/web-platform/tests/scroll-animations/css/timeline-range-name-offset-in-keyframes.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-animation.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-axis-computed.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-axis-parsing.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-delay-animation.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-dynamic.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-inset-animation.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-inset-computed.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-inset-parsing.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-lookup.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-name-computed.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-name-parsing.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-name-tree-scoped.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-shorthand.tentative.html
 create mode 100644 testing/web-platform/tests/scroll-animations/css/view-timeline-used-values.html

(limited to 'testing/web-platform/tests/scroll-animations/css')

diff --git a/testing/web-platform/tests/scroll-animations/css/animation-duration-auto.tentative.html b/testing/web-platform/tests/scroll-animations/css/animation-duration-auto.tentative.html
new file mode 100644
index 0000000000..f44a682890
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-duration-auto.tentative.html
@@ -0,0 +1,56 @@
+<!DOCTYPE html>
+<title>animation-duration: auto</title>
+<link rel="help" src="https://github.com/w3c/csswg-drafts/issues/6530">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="./support/testcommon.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+<style>
+  #scroller {
+    overflow: hidden;
+    width: 100px;
+    height: 100px;
+  }
+  #scroller > div {
+    height: 200px;
+    width: 200px;
+  }
+
+  @keyframes anim {
+    from { z-index: 0; }
+    to { z-index: 100; }
+  }
+
+  #scroller {
+    scroll-timeline: timeline;
+  }
+
+  #element {
+    z-index: -1;
+    animation-name: anim;
+    animation-duration: auto;
+    animation-timeline: timeline;
+  }
+</style>
+<main>
+  <div id=scroller>
+    <div></div>
+  </div>
+  <div id=element></div>
+</main>
+<script>
+  promise_test(async (t) => {
+    await waitForCSSScrollTimelineStyle();
+    assert_equals(getComputedStyle(element).zIndex, '0');
+  }, 'A value of auto can be specified for animation-duration');
+</script>
+
+<div id="target"></div>
+<script>
+  test_valid_value('animation-duration', 'auto');
+  test_computed_value('animation-duration', 'auto');
+  test_valid_value('animation', 'auto cubic-bezier(0, -2, 1, 3) -3s 4 reverse both paused anim');
+  test_computed_value('animation', 'auto cubic-bezier(0, -2, 1, 3) -3s 4 reverse both paused anim');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/animation-shorthand.html b/testing/web-platform/tests/scroll-animations/css/animation-shorthand.html
new file mode 100644
index 0000000000..60d6c76646
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-shorthand.html
@@ -0,0 +1,43 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-shorthand">
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script src="/css/support/shorthand-testcommon.js"></script>
+<div id="target"></div>
+<script>
+test_valid_value('animation',
+  '1s linear 1s 2 reverse forwards paused anim');
+
+test_invalid_value('animation',
+  '1s linear 1s 2 reverse forwards paused anim initial');
+test_invalid_value('animation',
+  '1s linear 1s 2 reverse forwards paused anim 2000');
+test_invalid_value('animation',
+  '1s linear 1s 2 reverse forwards paused anim scroll()');
+test_invalid_value('animation',
+  '1s linear 1s 2 reverse forwards paused anim view()');
+test_invalid_value('animation',
+  '1s linear 1s 2 reverse forwards paused anim timeline');
+
+test_computed_value('animation',
+  '1s linear 1s 2 reverse forwards paused anim');
+
+test_shorthand_value('animation',
+  `1s linear 1s 2 reverse forwards paused anim1,
+   1s linear 1s 2 reverse forwards paused anim2,
+   1s linear 1s 2 reverse forwards paused anim3`,
+{
+  'animation-duration': '1s, 1s, 1s',
+  'animation-timing-function': 'linear, linear, linear',
+  'animation-delay': '1s, 1s, 1s',
+  'animation-iteration-count': '2, 2, 2',
+  'animation-direction': 'reverse, reverse, reverse',
+  'animation-fill-mode': 'forwards, forwards, forwards',
+  'animation-play-state': 'paused, paused, paused',
+  'animation-name': 'anim1, anim2, anim3',
+  'animation-timeline': 'auto, auto, auto'
+});
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/animation-timeline-computed.html b/testing/web-platform/tests/scroll-animations/css/animation-timeline-computed.html
new file mode 100644
index 0000000000..9cabaab1fe
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-timeline-computed.html
@@ -0,0 +1,76 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#animation-timeline">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+</head>
+<style>
+  #outer { animation-timeline: foo; }
+  #target { animation-timeline: bar; }
+</style>
+<div id="outer">
+  <div id="target"></div>
+</div>
+<script>
+test_computed_value('animation-timeline', 'initial', 'auto');
+test_computed_value('animation-timeline', 'inherit', 'foo');
+test_computed_value('animation-timeline', 'unset', 'auto');
+test_computed_value('animation-timeline', 'revert', 'auto');
+test_computed_value('animation-timeline', 'auto');
+test_computed_value('animation-timeline', 'none');
+test_computed_value('animation-timeline', 'auto, auto');
+test_computed_value('animation-timeline', 'none, none');
+test_computed_value('animation-timeline', 'auto, none');
+test_computed_value('animation-timeline', 'none, auto');
+test_computed_value('animation-timeline', '"test"', 'test');
+test_computed_value('animation-timeline', '"none"');
+test_computed_value('animation-timeline', '"auto"');
+test_computed_value('animation-timeline', '"initial"');
+test_computed_value('animation-timeline', '"inherit"');
+test_computed_value('animation-timeline', '"unset"');
+test_computed_value('animation-timeline', '"revert"');
+test_computed_value('animation-timeline', '"revert-layer"');
+test_computed_value('animation-timeline', 'test');
+test_computed_value('animation-timeline', 'test1, test2');
+test_computed_value('animation-timeline', 'test1, "test2", none, test3, auto', 'test1, test2, none, test3, auto');
+
+test(() => {
+  let style = getComputedStyle(document.getElementById('target'));
+  assert_not_equals(Array.from(style).indexOf('animation-timeline'), -1);
+}, 'The animation-timeline property shows up in CSSStyleDeclaration enumeration');
+
+test(() => {
+  let style = document.getElementById('target').style;
+  assert_not_equals(style.cssText.indexOf('animation-timeline'), -1);
+}, 'The animation-timeline property shows up in CSSStyleDeclaration.cssText');
+
+// https://drafts.csswg.org/scroll-animations-1/#scroll-notation
+//
+// animation-timeline: scroll(<axis>? <scroller>?);
+// <axis> = block | inline | vertical | horizontal
+// <scroller> = root | nearest
+test_computed_value('animation-timeline', 'scroll()');
+test_computed_value('animation-timeline', 'scroll(block)', 'scroll()');
+test_computed_value('animation-timeline', 'scroll(inline)');
+test_computed_value('animation-timeline', 'scroll(horizontal)');
+test_computed_value('animation-timeline', 'scroll(vertical)');
+test_computed_value('animation-timeline', 'scroll(root)');
+test_computed_value('animation-timeline', 'scroll(nearest)', 'scroll()');
+test_computed_value('animation-timeline', 'scroll(inline nearest)', 'scroll(inline)');
+test_computed_value('animation-timeline', 'scroll(vertical root)');
+
+// https://drafts.csswg.org/scroll-animations-1/#view-notation
+test_computed_value('animation-timeline', 'view()');
+test_computed_value('animation-timeline', 'view(block)', 'view()');
+test_computed_value('animation-timeline', 'view(inline)', 'view(inline)');
+test_computed_value('animation-timeline', 'view(horizontal)', 'view(horizontal)');
+test_computed_value('animation-timeline', 'view(vertical)', 'view(vertical)');
+test_computed_value('animation-timeline', 'view(vertical 1px)');
+test_computed_value('animation-timeline', 'view(1px auto)');
+test_computed_value('animation-timeline', 'view(auto 1px)');
+test_computed_value('animation-timeline', 'view(vertical 1px auto)');
+test_computed_value('animation-timeline', 'view(1px vertical)', 'view(vertical 1px)');
+test_computed_value('animation-timeline', 'view(vertical auto)', 'view(vertical)');
+test_computed_value('animation-timeline', 'view(vertical auto auto)', 'view(vertical)');
+
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/animation-timeline-ignored.tentative.html b/testing/web-platform/tests/scroll-animations/css/animation-timeline-ignored.tentative.html
new file mode 100644
index 0000000000..32cb89c4ef
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-timeline-ignored.tentative.html
@@ -0,0 +1,145 @@
+<!DOCTYPE html>
+<link rel="help" src="https://github.com/w3c/csswg-drafts/pull/5666">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<style>
+  main {
+    overflow: hidden;
+    height: 0px;
+  }
+  main > div {
+    overflow: hidden;
+    width: 100px;
+    height: 100px;
+  }
+  main > div > div {
+    height: 200px;
+  }
+  @keyframes expand {
+    from { width: 100px; }
+    to { width: 200px; }
+  }
+  #scroller1 {
+    scroll-timeline: timeline1;
+  }
+  #scroller2 {
+    scroll-timeline: timeline2;
+  }
+  #scroller3 {
+    scroll-timeline: timeline3;
+  }
+  #element {
+    width: 0px;
+    height: 20px;
+    animation-name: expand;
+    animation-duration: 1000s;
+    animation-timing-function: linear;
+    animation-timeline: timeline1;
+  }
+  /* Ensure stable expectations if feature is not supported */
+  @supports not (animation-timeline:foo) {
+    #element { animation-play-state: paused; }
+  }
+</style>
+<main>
+  <div id=scroller1><div></div></div>
+  <div id=scroller2><div></div></div>
+  <div id=scroller3><div></div></div>
+  <div id=scroller4><div></div></div>
+  <div id=container></div>
+</main>
+<script>
+  // Force layout of scrollers.
+  scroller1.offsetTop;
+  scroller2.offsetTop;
+  scroller3.offsetTop;
+  scroller4.offsetTop;
+
+  scroller1.scrollTop = 20;
+  scroller2.scrollTop = 40;
+  scroller3.scrollTop = 60;
+  scroller4.scrollTop = 80;
+
+  // Create #element in #container, run |func|, then clean up afterwards.
+  function test_animation_timeline(func, description) {
+    promise_test(async () => {
+      try {
+        let element = document.createElement('element');
+        element.setAttribute('id', 'element');
+        container.append(element);
+        await func();
+      } finally {
+        while (container.firstChild)
+          container.firstChild.remove();
+      }
+    }, description);
+  }
+
+  test_animation_timeline(async () => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element).width, '120px');
+    element.style = 'animation-timeline:timeline2';
+    assert_equals(getComputedStyle(element).width, '140px');
+  }, 'Changing animation-timeline changes the timeline (sanity check)');
+
+  test_animation_timeline(async () => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element).width, '120px');
+
+    // Set a (non-CSS) ScrollTimeline on the CSSAnimation.
+    let timeline4 = new ScrollTimeline({
+      source: scroller4,
+      scrollOffsets: [CSS.px(0), CSS.px(100)]
+    });
+
+    element.getAnimations()[0].timeline = timeline4;
+    assert_equals(getComputedStyle(element).width, '180px');
+
+    // Changing the animation-timeline property should have no effect.
+    element.style = 'animation-timeline:timeline2';
+    assert_equals(getComputedStyle(element).width, '180px');
+  }, 'animation-timeline ignored after setting timeline with JS (ScrollTimeline from JS)');
+
+  test_animation_timeline(async () => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element).width, '120px');
+    let animation = element.getAnimations()[0];
+    let timeline1 = animation.timeline;
+
+    element.style = 'animation-timeline:timeline2';
+    assert_equals(getComputedStyle(element).width, '140px');
+
+    animation.timeline = timeline1;
+    assert_equals(getComputedStyle(element).width, '120px');
+
+    // Should have no effect.
+    element.style = 'animation-timeline:timeline3';
+    assert_equals(getComputedStyle(element).width, '120px');
+  }, 'animation-timeline ignored after setting timeline with JS (ScrollTimeline from CSS)');
+
+  test_animation_timeline(async () => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element).width, '120px');
+    element.getAnimations()[0].timeline = document.timeline;
+
+    // (The animation continues from where the previous timeline left it).
+    assert_equals(getComputedStyle(element).width, '120px');
+
+    // Changing the animation-timeline property should have no effect.
+    element.style = 'animation-timeline:timeline2';
+    assert_equals(getComputedStyle(element).width, '120px');
+  }, 'animation-timeline ignored after setting timeline with JS (document timeline)');
+
+  test_animation_timeline(async () => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element).width, '120px');
+    element.getAnimations()[0].timeline = null;
+    assert_equals(getComputedStyle(element).width, '0px');
+
+    // Changing the animation-timeline property should have no effect.
+    element.style = 'animation-timeline:timeline2';
+    assert_equals(getComputedStyle(element).width, '0px');
+  }, 'animation-timeline ignored after setting timeline with JS (null)');
+
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/animation-timeline-in-keyframe.html b/testing/web-platform/tests/scroll-animations/css/animation-timeline-in-keyframe.html
new file mode 100644
index 0000000000..7548333139
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-timeline-in-keyframe.html
@@ -0,0 +1,27 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#animation-timeline">
+<link rel="help" href="https://drafts.csswg.org/css-animations-1/#keyframes">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+</head>
+<style>
+  @keyframes test {
+    from { width: 100px; animation-timeline: foo; }
+    to { width: 100px; animation-timeline: foo; }
+  }
+  #target {
+    width: 50px;
+    animation-name: test;
+    animation-duration: 1s;
+    animation-play-state: paused;
+  }
+</style>
+<div id="target"></div>
+<script>
+test(() => {
+  let style = getComputedStyle(document.getElementById('target'));
+  // Checking 'width' verifies that the animation is applied at all.
+  assert_equals(style.width, '100px');
+  assert_equals(style.animationTimeline, 'auto');
+}, 'The animation-timeline property may not be used in keyframes');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/animation-timeline-multiple.html b/testing/web-platform/tests/scroll-animations/css/animation-timeline-multiple.html
new file mode 100644
index 0000000000..8ae37bf751
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-timeline-multiple.html
@@ -0,0 +1,90 @@
+<!DOCTYPE html>
+<title>animation-timeline with multiple timelines</title>
+<link rel="help" src="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<style>
+  main > div {
+    overflow: hidden;
+    width: 100px;
+    height: 100px;
+  }
+  main > div > div {
+    height: 200px;
+    width:  200px;
+  }
+
+  @keyframes top {
+    from { top: 100px; }
+    to { top: 200px; }
+  }
+  @keyframes bottom {
+    from { bottom: 100px; }
+    to { bottom: 200px; }
+  }
+  @keyframes left {
+    from { left: 100px; }
+    to { left: 200px; }
+  }
+  @keyframes right {
+    from { right: 100px; }
+    to { right: 200px; }
+  }
+
+  #top_scroller {
+    scroll-timeline: block top_timeline;
+  }
+  #bottom_scroller {
+    scroll-timeline: inline bottom_timeline;
+  }
+  #left_scroller {
+    scroll-timeline: block left_timeline;
+  }
+  #right_scroller {
+    scroll-timeline: inline right_timeline;
+  }
+
+  #element {
+    animation-name: top, bottom, left, right;
+    animation-duration: 10s;
+    animation-timing-function: linear;
+    animation-timeline: top_timeline, bottom_timeline, left_timeline, right_timeline;
+  }
+  /* Ensure stable expectations if feature is not supported */
+  @supports not (animation-timeline:foo) {
+    #element { animation-play-state: paused; }
+  }
+</style>
+<main>
+  <div id=top_scroller><div></div></div>
+  <div id=bottom_scroller><div></div></div>
+  <div id=left_scroller><div></div></div>
+  <div id=right_scroller><div></div></div>
+  <div id=element></div>
+</main>
+<script>
+  // Force layout of scrollers.
+  top_scroller.offsetTop;
+  bottom_scroller.offsetTop;
+  left_scroller.offsetTop;
+  right_scroller.offsetTop;
+
+  top_scroller.scrollTop = 20;
+  top_scroller.scrollLeft = 40;
+  bottom_scroller.scrollTop = 20;
+  bottom_scroller.scrollLeft = 40;
+  left_scroller.scrollTop = 60;
+  left_scroller.scrollLeft = 80;
+  right_scroller.scrollTop = 60;
+  right_scroller.scrollLeft = 80;
+
+  promise_test(async (t) => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element).top, '120px');
+    assert_equals(getComputedStyle(element).bottom, '140px');
+    assert_equals(getComputedStyle(element).left, '160px');
+    assert_equals(getComputedStyle(element).right, '180px');
+  }, 'animation-timeline works with multiple timelines');
+
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/animation-timeline-named-scroll-progress-timeline.tentative.html b/testing/web-platform/tests/scroll-animations/css/animation-timeline-named-scroll-progress-timeline.tentative.html
new file mode 100644
index 0000000000..9f55e2d2c9
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-timeline-named-scroll-progress-timeline.tentative.html
@@ -0,0 +1,662 @@
+<!DOCTYPE html>
+<title>The animation-timeline: scroll-timeline-name</title>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/rewrite#scroll-timelines-named">
+<link rel="help" src="https://github.com/w3c/csswg-drafts/issues/6674">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { translate: 50px; }
+    to { translate: 150px; }
+  }
+  #target {
+    width: 100px;
+    height: 100px;
+  }
+  .square {
+    width: 100px;
+    height: 100px;
+  }
+  .square-container {
+    width: 300px;
+    height: 300px;
+  }
+  .scroller {
+    overflow: scroll;
+  }
+  .content {
+    inline-size: 100%;
+    block-size: 100%;
+    padding-inline-end: 100px;
+    padding-block-end: 100px;
+  }
+</style>
+<body>
+<div id="log"></div>
+<script>
+"use strict";
+
+setup(assert_implements_animation_timeline);
+
+function createScroller(t, scrollerSizeClass) {
+  let scroller = document.createElement('div');
+  let className = scrollerSizeClass || 'square';
+  scroller.className = `scroller ${className}`;
+  let content = document.createElement('div');
+  content.className = 'content';
+
+  scroller.appendChild(content);
+
+  t.add_cleanup(function() {
+    content.remove();
+    scroller.remove();
+  });
+
+  return scroller;
+}
+
+function createTarget(t) {
+  let target = document.createElement('div');
+  target.id = 'target';
+
+  t.add_cleanup(function() {
+    target.remove();
+  });
+
+  return target;
+}
+
+function createScrollerAndTarget(t, scrollerSizeClass) {
+  return [createScroller(t, scrollerSizeClass), createTarget(t)];
+}
+
+// -------------------------
+// Test scroll-timeline-name
+// -------------------------
+
+promise_test(async t => {
+  let target = document.createElement('div');
+  target.id = 'target';
+  target.className = 'scroller';
+  let content = document.createElement('div');
+  content.className = 'content';
+
+  // <div id='target' class='scroller'>
+  //   <div id='content'></div>
+  // </div>
+  document.body.appendChild(target);
+  target.appendChild(content);
+
+  target.style.scrollTimelineName = 'timeline';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  target.scrollTop = 50; // 50%, in [0, 100].
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '100px');
+
+  content.remove();
+  target.remove();
+}, 'scroll-timeline-name is referenceable in animation-timeline on the ' +
+   'declaring element itself');
+
+promise_test(async t => {
+  let [parent, target] = createScrollerAndTarget(t, 'square-container');
+
+  // <div id='parent' class='scroller'>
+  //   <div id='target'></div>
+  //   <div id='content'></div>
+  // </div>
+  document.body.appendChild(parent);
+  parent.insertBefore(target, parent.firstElementChild);
+
+  parent.style.scrollTimelineName = 'timeline';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  parent.scrollTop = 100; // 50%, in [0, 200].
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, "scroll-timeline-name is referenceable in animation-timeline on that " +
+   "element's descendants");
+
+promise_test(async t => {
+  let [sibling, target] = createScrollerAndTarget(t);
+
+  // <div id='sibling' class='scroller'> ... </div>
+  // <div id='target'></div>
+  document.body.appendChild(sibling);
+  document.body.appendChild(target);
+
+  sibling.style.scrollTimelineName = 'timeline';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  sibling.scrollTop = 50; // 50%, in [0, 100].
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, "scroll-timeline-name is referenceable in animation-timeline on that " +
+   "element's following siblings");
+
+promise_test(async t => {
+  let [sibling, target] = createScrollerAndTarget(t);
+  let parent = document.createElement('div');
+
+  // <div id='sibling' class='scroller'> ... </div>
+  // <div id='parent'>
+  //   <div id='target'></div>
+  // </div>
+  document.body.appendChild(sibling);
+  document.body.appendChild(parent);
+  parent.appendChild(target);
+
+  sibling.style.scrollTimelineName = 'timeline';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  sibling.scrollTop = 50; // 50%, in [0, 100].
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '100px');
+
+  parent.remove();
+}, "scroll-timeline-name is referenceable in animation-timeline on that " +
+   "element's following siblings' descendants");
+
+// FIXME: We may use global scope for scroll-timeline-name.
+// See https://github.com/w3c/csswg-drafts/issues/7047
+promise_test(async t => {
+  let [sibling, target] = createScrollerAndTarget(t);
+
+  // <div id='target'></div>
+  // <div id='sibling' class='scroller'> ... </div>
+  document.body.appendChild(target);
+  document.body.appendChild(sibling);
+
+  sibling.style.scrollTimelineName = 'timeline';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  sibling.scrollTop = 50; // 50%, in [0, 100].
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '50px',
+    'Animation with unknown timeline name holds current time at zero');
+}, "scroll-timeline-name is not referenceable in animation-timeline on that " +
+   "element's previous siblings");
+
+promise_test(async t => {
+  let [sibling, target] = createScrollerAndTarget(t);
+  let parent = document.createElement('div');
+  parent.className = 'scroller square-container';
+  let content = document.createElement('div');
+  content.className = 'content';
+
+  // <div id='parent' class='scroller'>
+  //   <div id='sibling' class='scroller'> ... </div>
+  //   <div id='target'></div>
+  //   <div id='content'></div>
+  // </div>
+  document.body.appendChild(parent);
+  parent.appendChild(sibling);
+  parent.appendChild(target);
+  parent.appendChild(content);
+
+  parent.style.scrollTimelineName = 'timeline';
+  parent.style.scrollTimelineAxis = 'inline';
+  sibling.style.scrollTimelineName = 'timeline';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  parent.scrollTop = 50; // 25%, in [0, 200].
+  sibling.scrollTop = 50; // 50%, in [0, 100].
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '100px');
+
+  content.remove();
+  parent.remove();
+}, 'scroll-timeline-name is matched based on tree order, which considers ' +
+   'siblings closer than parents');
+
+promise_test(async t => {
+  let sibling = document.createElement('div');
+  sibling.className = 'square';
+  sibling.style.overflowX = 'clip'; // This makes overflow-y be clip as well.
+  let target = document.createElement('div');
+  target.id = 'target';
+
+  // <div id='sibling' style='overflow-x: clip'></div>
+  // <div id='target'></div>
+  document.body.appendChild(sibling);
+  document.body.appendChild(target);
+
+  sibling.style.scrollTimelineName = 'timeline';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  sibling.scrollTop = 50; // 50%, in [0, 100].
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, 'none',
+    'Animation with an unresolved current time');
+
+  target.remove();
+  sibling.remove();
+}, 'scroll-timeline-name on an element which is not a scroll-container');
+
+promise_test(async t => {
+  let [sibling, target] = createScrollerAndTarget(t);
+  let main = document.createElement('div');
+  main.id = 'name';
+
+  // <div id='main'>
+  //   <div id='sibling' class='scroller'> ... </div>
+  //   <div id='target'></div>
+  // </div>
+  document.body.appendChild(main);
+  main.appendChild(sibling);
+  main.appendChild(target);
+
+  target.style.animation = 'anim 10s linear';
+  target.style.animationTimeline = 'timeline';
+  sibling.scrollTop = 50; // 50%, in [50, 150].
+  await waitForNextFrame();
+
+  // Unknown animation-timeline, current time held at zero.
+  assert_equals(getComputedStyle(target).translate, '50px');
+
+  // Ensure that #main (an ancestor of the scroller) needs style recalc.
+  main.style.background = 'lightgray';
+  sibling.style.scrollTimelineName = 'timeline';
+  await waitForCSSScrollTimelineStyle();
+  assert_equals(getComputedStyle(target).translate, '100px');
+
+  main.remove();
+}, 'scroll-timeline-name affects subsequent siblings when changed');
+
+promise_test(async t => {
+  let target = createTarget(t);
+
+  // <div id='target'></div>
+  document.body.appendChild(target);
+
+  target.style.animation = 'anim 10s linear';
+  target.style.animationTimeline = 'timeline';
+
+  // Unknown animation-timeline, current time held at zero.
+  assert_equals(getComputedStyle(target).translate, '50px');
+
+  let scroller = createScroller(t);
+  // <div class='scroller'> ... </div>
+  // <div id='target'></div>
+  document.body.insertBefore(scroller, target);
+  scroller.style.scrollTimelineName = 'timeline';
+
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '50px');
+
+  // Ensure that time is not just held at zero.
+  scroller.scrollTop = 50; // 50%, in [50, 150].
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, 'scroll-timeline-name on inserted element affects subsequent siblings');
+
+promise_test(async t => {
+  let [scroller, target] = createScrollerAndTarget(t);
+
+  // <div class='scroller'> ... </div>
+  // <div id='target'></div>
+  document.body.appendChild(scroller);
+  document.body.appendChild(target);
+
+  scroller.scrollTop = 50; // 50%, in [50, 150].
+  await waitForNextFrame();
+
+  scroller.style.scrollTimelineName = 'timeline';
+  target.style.animation = 'anim 10s linear';
+  target.style.animationTimeline = 'timeline';
+  await waitForCSSScrollTimelineStyle();
+
+  assert_equals(getComputedStyle(target).translate, '100px');
+
+  // This effectively removes the CSS-created ScrollTimeline on this element,
+  // thus invoking "setting the timeline of an animation" [1] with a null-
+  // timeline on affected elements. This in turn causes the current time to
+  // become unresolved [2], ultimately resulting in no effect value.
+  //
+  // [1] https://drafts.csswg.org/web-animations-1/#setting-the-timeline
+  // [2] https://drafts.csswg.org/web-animations-1/#the-current-time-of-an-animation
+  scroller.remove();
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, 'none');
+}, 'scroll-timeline-name on removed element affects subsequent siblings');
+
+promise_test(async t => {
+  let [scroller, target] = createScrollerAndTarget(t);
+
+  // <div class='scroller' style='display:none'> ... </div>
+  // <div id='target'></div>
+  scroller.style.display = 'none';
+  document.body.appendChild(scroller);
+  document.body.appendChild(target);
+
+  scroller.style.scrollTimelineName = 'timeline';
+  target.style.animation = 'anim 10s linear';
+  target.style.animationTimeline = 'timeline';
+
+  // Unknown animation-timeline, current time held at zero.
+  assert_equals(getComputedStyle(target).translate, '50px');
+
+  scroller.style.display = 'block';
+  scroller.scrollTop = 50; // 50%, in [50, 150].
+  await waitForNextFrame();
+
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, 'scroll-timeline-name on element leaving display:none affects subsequent siblings');
+
+promise_test(async t => {
+  let [scroller, target] = createScrollerAndTarget(t);
+
+  // <div class='scroller'> ... </div>
+  // <div id='target'></div>
+  document.body.appendChild(scroller);
+  document.body.appendChild(target);
+
+  scroller.scrollTop = 50; // 50%, in [50, 150].
+  await waitForNextFrame();
+
+  scroller.style.scrollTimelineName = 'timeline';
+  target.style.animation = 'anim 10s linear';
+  target.style.animationTimeline = 'timeline';
+  await waitForCSSScrollTimelineStyle();
+
+  assert_equals(getComputedStyle(target).translate, '100px');
+
+  // See comment in the test "scroll-timeline-name on removed element ..." for
+  // an explantation of this result. (Setting display:none is similar to
+  // removing the element).
+  scroller.style.display = 'none';
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, 'none');
+}, 'scroll-timeline-name on element becoming display:none affects subsequent siblings');
+
+promise_test(async t => {
+  let [scroller, target] = createScrollerAndTarget(t);
+
+  // <div id='scroller' class='scroller'> ... </div>
+  // <div id='target'></div>
+
+  document.body.appendChild(scroller);
+  document.body.appendChild(target);
+
+  scroller.style.scrollTimelineName = 'timeline';
+  scroller.style.display = 'none';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  await waitForNextFrame();
+
+  const anim = target.getAnimations()[0];
+  assert_true(!!anim, 'Failed to create animation');
+  assert_equals(anim.timeline, null);
+  // Hold time of animation is zero.
+  assert_equals(getComputedStyle(target).translate, '50px');
+
+  scroller.style.display = 'block';
+  scroller.scrollTop = 50;
+  await waitForNextFrame();
+
+  assert_true(!!anim.timeline, 'Failed to create timeline');
+  assert_equals(getComputedStyle(target).translate, '100px');
+
+}, 'scroll-timeline-name on element not resolved until element becomes visible');
+
+promise_test(async t => {
+  let [scroller, target] = createScrollerAndTarget(t);
+
+  // <div id='scroller' class='scroller'> ... </div>
+  // <div id='target'></div>
+
+  document.body.appendChild(scroller);
+  document.body.appendChild(target);
+
+  scroller.style.scrollTimelineName = 'timeline-A';
+  scroller.scrollTop = 50;
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline-B';
+
+  await waitForNextFrame();
+
+  const anim = target.getAnimations()[0];
+  assert_true(!!anim, 'Failed to create animation');
+  assert_equals(anim.timeline, null);
+  // Hold time of animation is zero.
+  assert_equals(getComputedStyle(target).translate, '50px');
+
+  scroller.style.scrollTimelineName = 'timeline-B';
+  await waitForNextFrame();
+
+  assert_true(!!anim.timeline, 'Failed to create timeline');
+  assert_equals(getComputedStyle(target).translate, '100px');
+
+}, 'Change in scroll-timeline-name to match animation timeline updates animation.');
+
+promise_test(async t => {
+  let [scroller, target] = createScrollerAndTarget(t);
+
+  // <div id='scroller' class='scroller'> ... </div>
+  // <div id='target'></div>
+
+  document.body.appendChild(scroller);
+  document.body.appendChild(target);
+
+  scroller.style.scrollTimelineName = 'timeline-A';
+  scroller.scrollTop = 50;
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline-A';
+
+  await waitForNextFrame();
+
+  const anim = target.getAnimations()[0];
+  assert_true(!!anim, 'Failed to create animation');
+  assert_true(!!anim.timeline, 'Failed to create timeline');
+  assert_equals(getComputedStyle(target).translate, '100px');
+
+  scroller.style.scrollTimelineName = 'timeline-B';
+  await waitForNextFrame();
+
+  assert_equals(anim.timeline, null, 'Failed to remove timeline');
+  assert_equals(getComputedStyle(target).translate, 'none');
+
+}, 'Change in scroll-timeline-name to no longer match animation timeline updates animation.');
+
+promise_test(async t => {
+  let target = createTarget(t);
+  let scroller1 = createScroller(t);
+  let scroller2 = createScroller(t);
+
+  target.style.animation = 'anim 10s linear';
+  target.style.animationTimeline = 'timeline';
+  scroller1.style.scrollTimelineName = 'timeline';
+  scroller2.style.scrollTimelineName = 'timeline';
+  scroller1.id = 'A';
+  scroller2.id = 'B';
+
+  // <div class='scroller' id='A'> ... </div> (scroller1)
+  // <div class='scroller' id="B"> ... </div> (scroller2)
+  // <div id='target'></div>
+  document.body.appendChild(scroller1);
+  document.body.appendChild(scroller2);
+  document.body.append(target);
+
+  scroller1.scrollTop = 10; // 10%, in [50, 150].
+  scroller2.scrollTop = 50; // 50%, in [50, 150].
+  await waitForNextFrame();
+
+
+  // The named timeline lookup should select scroller2.
+  let anim = target.getAnimations()[0];
+  assert_true(!!anim, 'Failed to fetch animation');
+  assert_equals(anim.timeline.source.id, 'B');
+  assert_equals(getComputedStyle(target).translate, '100px');
+
+  scroller2.remove();
+
+  // Now it should select scroller1.
+  anim = target.getAnimations()[0];
+  assert_true(!!anim, 'Failed to fetch animation after update');
+  assert_true(!!anim.timeline, 'Animation no longer has a timeline');
+  assert_equals(anim.timeline.source.id, 'A', 'Timeline not updated');
+  assert_equals(getComputedStyle(target).translate, '60px');
+}, 'Timeline lookup finds next candidate when element is removed');
+
+promise_test(async t => {
+  let target = createTarget(t);
+  let scroller1 = createScroller(t);
+
+  target.style.animation = 'anim 10s linear';
+  target.style.animationTimeline = 'timeline';
+  scroller1.style.scrollTimelineName = 'timeline';
+  scroller1.id = 'A';
+
+  // <div class='scroller' id='A'> ... </div> (scroller1)
+  // <div id='target'></div>
+  document.body.appendChild(scroller1);
+  document.body.append(target);
+
+  scroller1.scrollTop = 10; // 10%, in [50, 150].
+
+  await waitForNextFrame();
+
+  const anim = target.getAnimations()[0];
+
+  assert_true(!!anim.timeline, 'Failed to retrieve animation');
+  assert_equals(anim.timeline.source.id, 'A');
+  assert_equals(getComputedStyle(target).translate, '60px');
+
+  await waitForNextFrame();
+
+  let scroller2 = createScroller(t);
+  scroller2.style.scrollTimelineName = 'timeline';
+  scroller2.id = 'B';
+
+  // <div class='scroller' id="A"> ... </div> (scroller1)
+  // <div class='scroller' id="B"> ... </div> (scroller2)
+  // <div id='target'></div>
+  document.body.insertBefore(scroller2, target);
+
+  scroller2.scrollTop = 50; // 50%, in [50, 150].
+
+  await waitForNextFrame();
+
+  // The timeline should be updated to scroller2.
+  assert_true(!!anim.timeline, 'Animation no longer has a timeline');
+  assert_equals(anim.timeline.source.id, 'B', 'Timeline not updated');
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, 'Timeline lookup updates candidate when closer match available.');
+
+promise_test(async t => {
+  let target = createTarget(t);
+
+  // <div id='target'></div>
+  document.body.append(target);
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  await waitForNextFrame();
+
+  // Timeline initially cannot be resolved, resulting in a null
+  // timeline. The animation's hold time is zero.
+  let anim = document.getAnimations()[0];
+  assert_equals(getComputedStyle(target).translate, '50px');
+
+  await waitForNextFrame();
+
+  let scroller = createScroller(t);
+  scroller.style.scrollTimelineName = 'timeline';
+
+  // <div class='scroller'> ... </div> (scroller1)
+  // <div id='target'></div>
+  document.body.insertBefore(scroller, target);
+
+  scroller.scrollTop = 50; // 50%, in [50, 150].
+
+  await waitForNextFrame();
+
+  // The timeline should be updated to scroller.
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, 'Timeline lookup updates candidate when match becomes available.');
+
+// -------------------------
+// Test scroll-timeline-axis
+// -------------------------
+
+promise_test(async t => {
+  let [scroller, target] = createScrollerAndTarget(t);
+  scroller.style.writingMode = 'vertical-lr';
+
+  document.body.appendChild(scroller);
+  document.body.appendChild(target);
+
+  scroller.style.scrollTimeline = 'timeline block';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  scroller.scrollLeft = 50;
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, 'scroll-timeline-axis is block');
+
+promise_test(async t => {
+  let [scroller, target] = createScrollerAndTarget(t);
+  scroller.style.writingMode = 'vertical-lr';
+
+  document.body.appendChild(scroller);
+  document.body.appendChild(target);
+
+  scroller.style.scrollTimeline = 'timeline inline';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  scroller.scrollTop = 50;
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, 'scroll-timeline-axis is inline');
+
+promise_test(async t => {
+  let [scroller, target] = createScrollerAndTarget(t);
+  scroller.style.writingMode = 'vertical-lr';
+
+  document.body.appendChild(scroller);
+  document.body.appendChild(target);
+
+  scroller.style.scrollTimeline = 'timeline horizontal';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  scroller.scrollLeft = 50;
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, 'scroll-timeline-axis is horizontal');
+
+promise_test(async t => {
+  let [scroller, target] = createScrollerAndTarget(t);
+  scroller.style.writingMode = 'vertical-lr';
+
+  document.body.appendChild(scroller);
+  document.body.appendChild(target);
+
+  scroller.style.scrollTimeline = 'timeline vertical';
+  target.style.animation = "anim 10s linear";
+  target.style.animationTimeline = 'timeline';
+
+  scroller.scrollTop = 50;
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, 'scroll-timeline-axis is vertical');
+
+// TODO: Add more tests which change scroll-timeline-axis property.
+// Those animations which use this timeline should be restyled properly.
+
+</script>
+</body>
diff --git a/testing/web-platform/tests/scroll-animations/css/animation-timeline-none.html b/testing/web-platform/tests/scroll-animations/css/animation-timeline-none.html
new file mode 100644
index 0000000000..a8e07a44d6
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-timeline-none.html
@@ -0,0 +1,41 @@
+<!DOCTYPE html>
+<link rel="help" src="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<link rel="help" src="https://drafts.csswg.org/web-animations/#playing-an-animation-section">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<style>
+  @keyframes expand {
+    from { width: 100px; }
+    to { width: 200px; }
+  }
+
+  .test {
+    width: 0px;
+    animation-name: expand;
+    animation-duration: 1s;
+  }
+
+  #element_timeline_none {
+    animation-timeline: none;
+  }
+  #element_unknown_timeline {
+    animation-timeline: unknown_timeline;
+  }
+
+</style>
+<div class=test id=element_timeline_none></div>
+<div class=test id=element_unknown_timeline></div>
+<script>
+  promise_test(async (t) => {
+    assert_equals(getComputedStyle(element_timeline_none).width, '100px');
+    await waitForAnimationFrames(3);
+    assert_equals(getComputedStyle(element_timeline_none).width, '100px');
+  }, 'Animation with animation-timeline:none holds current time at zero');
+
+  promise_test(async (t) => {
+    assert_equals(getComputedStyle(element_unknown_timeline).width, '100px');
+    await waitForAnimationFrames(3);
+    assert_equals(getComputedStyle(element_unknown_timeline).width, '100px');
+  }, 'Animation with unknown timeline name holds current time at zero');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/animation-timeline-parsing.html b/testing/web-platform/tests/scroll-animations/css/animation-timeline-parsing.html
new file mode 100644
index 0000000000..1a30f11f85
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-timeline-parsing.html
@@ -0,0 +1,88 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#animation-timeline">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+</head>
+<div id="target"></div>
+<script>
+test_valid_value('animation-timeline', 'initial');
+test_valid_value('animation-timeline', 'inherit');
+test_valid_value('animation-timeline', 'unset');
+test_valid_value('animation-timeline', 'revert');
+test_valid_value('animation-timeline', 'auto');
+test_valid_value('animation-timeline', 'none');
+test_valid_value('animation-timeline', 'auto, auto');
+test_valid_value('animation-timeline', 'none, none');
+test_valid_value('animation-timeline', 'auto, none');
+test_valid_value('animation-timeline', 'none, auto');
+test_valid_value('animation-timeline', '"test"', ["test", '"test"']);
+test_valid_value('animation-timeline', '"none"');
+test_valid_value('animation-timeline', '"auto"');
+test_valid_value('animation-timeline', '"initial"');
+test_valid_value('animation-timeline', '"inherit"');
+test_valid_value('animation-timeline', '"unset"');
+test_valid_value('animation-timeline', '"revert"');
+test_valid_value('animation-timeline', 'test');
+test_valid_value('animation-timeline', 'test1, test2');
+test_valid_value('animation-timeline', 'test1, "test2", none, test3, auto', ["test1, test2, none, test3, auto", 'test1, "test2", none, test3, auto']);
+
+test_invalid_value('animation-timeline', '10px');
+test_invalid_value('animation-timeline', 'auto auto');
+test_invalid_value('animation-timeline', 'none none');
+test_invalid_value('animation-timeline', 'foo bar');
+test_invalid_value('animation-timeline', '"foo" "bar"');
+test_invalid_value('animation-timeline', 'rgb(1, 2, 3)');
+test_invalid_value('animation-timeline', '#fefefe');
+
+// https://drafts.csswg.org/scroll-animations-1/#scroll-notation
+//
+// animation-timeline: scroll(<axis>? <scroller>?);
+// <axis> = block | inline | vertical | horizontal
+// <scroller> = root | nearest
+test_valid_value('animation-timeline', 'scroll()');
+test_valid_value('animation-timeline', 'scroll(block)', 'scroll()');
+test_valid_value('animation-timeline', 'scroll(inline)');
+test_valid_value('animation-timeline', 'scroll(horizontal)');
+test_valid_value('animation-timeline', 'scroll(vertical)');
+test_valid_value('animation-timeline', 'scroll(root)');
+test_valid_value('animation-timeline', 'scroll(nearest)', 'scroll()');
+test_valid_value('animation-timeline', 'scroll(inline nearest)', 'scroll(inline)');
+test_valid_value('animation-timeline', 'scroll(vertical root)');
+
+test_invalid_value('animation-timeline', 'scroll(root block)');
+test_invalid_value('animation-timeline', 'scroll(abc root)');
+test_invalid_value('animation-timeline', 'scroll(abc)');
+test_invalid_value('animation-timeline', 'scroll(vertical abc)');
+test_invalid_value('animation-timeline', 'scroll("string")');
+
+// https://drafts.csswg.org/scroll-animations-1/#view-notation
+test_valid_value('animation-timeline', 'view()');
+test_valid_value('animation-timeline', 'view(block)', 'view()');
+test_valid_value('animation-timeline', 'view(inline)');
+test_valid_value('animation-timeline', 'view(horizontal)');
+test_valid_value('animation-timeline', 'view(vertical)');
+test_valid_value('animation-timeline', 'view(vertical 1px 2px)');
+test_valid_value('animation-timeline', 'view(vertical 1px)');
+test_valid_value('animation-timeline', 'view(vertical auto)', 'view(vertical)');
+test_valid_value('animation-timeline', 'view(vertical auto auto)', 'view(vertical)');
+test_valid_value('animation-timeline', 'view(vertical auto 1px)');
+test_valid_value('animation-timeline', 'view(1px 2px vertical)', 'view(vertical 1px 2px)');
+test_valid_value('animation-timeline', 'view(1px vertical)', 'view(vertical 1px)');
+test_valid_value('animation-timeline', 'view(auto horizontal)', 'view(horizontal)');
+test_valid_value('animation-timeline', 'view(1px 2px)');
+test_valid_value('animation-timeline', 'view(1px)');
+test_valid_value('animation-timeline', 'view(1px 1px)', 'view(1px)');
+test_valid_value('animation-timeline', 'view(1px auto)');
+test_valid_value('animation-timeline', 'view(auto calc(1% + 1px))');
+test_valid_value('animation-timeline', 'view(auto)', 'view()');
+test_valid_value('animation-timeline', 'view(auto auto)', 'view()');
+
+test_invalid_value('animation-timeline', 'view(vertical 1px 2px 3px)');
+test_invalid_value('animation-timeline', 'view(1px vertical 3px)');
+test_invalid_value('animation-timeline', 'view(1px 2px 3px)');
+test_invalid_value('animation-timeline', 'view(abc block)');
+test_invalid_value('animation-timeline', 'view(abc)');
+test_invalid_value('animation-timeline', 'view(vertical abc)');
+test_invalid_value('animation-timeline', 'view("string")');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/animation-timeline-scroll-functional-notation.tentative.html b/testing/web-platform/tests/scroll-animations/css/animation-timeline-scroll-functional-notation.tentative.html
new file mode 100644
index 0000000000..e28e85245e
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-timeline-scroll-functional-notation.tentative.html
@@ -0,0 +1,148 @@
+<!DOCTYPE html>
+<title>The animation-timeline: scroll() notation</title>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/rewrite#scroll-notation">
+<link rel="help" src="https://github.com/w3c/csswg-drafts/issues/6674">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { translate: 50px; }
+    to { translate: 150px; }
+  }
+  html {
+    min-height: 100vh;
+    /* This makes the max scrollable ragne be 100px in root element */
+    padding-bottom: 100px;
+  }
+  #container {
+    width: 300px;
+    height: 300px;
+    overflow: scroll;
+  }
+  #target {
+    width: 100px;
+    /* This makes the max scrollable ragne be 100px in the block direction */
+    height: 100px;
+  }
+  /* large block content */
+  .block-content {
+    block-size: 100%;
+  }
+  /* large inline content */
+  .inline-content {
+    inline-size: 100%;
+    block-size: 5px;
+    /* This makes the max scrollable ragne be 100px in the inline direction */
+    padding-inline-end: 100px;
+  }
+</style>
+<body>
+<div id="log"></div>
+<script>
+"use strict";
+
+setup(assert_implements_animation_timeline);
+
+const root = document.scrollingElement;
+const createTargetWithStuff = function(t, contentClass) {
+  let container = document.createElement('div');
+  container.id = 'container';
+  let target = document.createElement('div');
+  target.id = 'target';
+  let content = document.createElement('div');
+  content.className = contentClass;
+
+  // <div id='container'>
+  //   <div id='target'></div>
+  //   <div class=contentClass></div>
+  // </div>
+  document.body.appendChild(container);
+  container.appendChild(target);
+  container.appendChild(content);
+
+  if (t && typeof t.add_cleanup === 'function') {
+    t.add_cleanup(() => {
+      content.remove();
+      target.remove();
+      container.remove();
+    });
+  }
+
+  return [container, target];
+};
+
+async function scrollLeft(element, value) {
+  element.scrollLeft = value;
+  await waitForNextFrame();
+}
+
+async function scrollTop(element, value) {
+  element.scrollTop = value;
+  await waitForNextFrame();
+}
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, 'block-content');
+  div.style.animation = "anim 10s linear";
+  div.style.animationTimeline = "scroll(nearest)";
+
+  await scrollTop(root, 50);
+  assert_equals(getComputedStyle(div).translate, '50px');
+
+  await scrollTop(container, 50);
+  assert_equals(getComputedStyle(div).translate, '100px');
+
+  await scrollTop(root, 0);
+}, 'animation-timeline: scroll(nearest)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, 'block-content');
+  div.style.animation = "anim 10s linear";
+  div.style.animationTimeline = "scroll(root)";
+
+  await scrollTop(container, 50);
+  assert_equals(getComputedStyle(div).translate, '50px');
+
+  await scrollTop(root, 50);
+  assert_equals(getComputedStyle(div).translate, '100px');
+
+  await scrollTop(root, 0);
+}, 'animation-timeline: scroll(root)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, 'inline-content');
+  div.style.animation = "anim 10s linear";
+  div.style.animationTimeline = "scroll(inline)";
+
+  await scrollLeft(container, 50);
+  assert_equals(getComputedStyle(div).translate, '100px');
+}, 'animation-timeline: scroll(inline)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, 'block-content');
+  container.style.writingMode = 'vertical-lr';
+  div.style.animation = "anim 10s linear";
+  div.style.animationTimeline = "scroll(horizontal)";
+
+  await scrollLeft(container, 50);
+  assert_equals(getComputedStyle(div).translate, '100px');
+}, 'animation-timeline: scroll(horizontal)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, 'inline-content');
+  container.style.writingMode = 'vertical-lr';
+  div.style.animation = "anim 10s linear";
+  div.style.animationTimeline = "scroll(vertical)";
+
+  await scrollTop(container, 50);
+  assert_equals(getComputedStyle(div).translate, '100px');
+}, 'animation-timeline: scroll(vertical)');
+
+// TODO: Add more tests which change the overflow property of the container for
+// scroll(nearest)
+
+</script>
+</body>
diff --git a/testing/web-platform/tests/scroll-animations/css/animation-timeline-view-functional-notation.tentative.html b/testing/web-platform/tests/scroll-animations/css/animation-timeline-view-functional-notation.tentative.html
new file mode 100644
index 0000000000..d93306819a
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/animation-timeline-view-functional-notation.tentative.html
@@ -0,0 +1,263 @@
+<!DOCTYPE html>
+<title>The animation-timeline: view() notation</title>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<link rel="help" src="https://w3c.github.io/csswg-drafts/scroll-animations-1/#view-notation">
+<link rel="help" src="https://github.com/w3c/csswg-drafts/issues/7587">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes fade-in-out {
+    enter 0% { opacity: 0; }
+    enter 100% { opacity: 1; }
+    exit 0% { opacity: 1; }
+    exit 100% { opacity: 0; }
+  }
+  @keyframes fade-out {
+    exit 0% { opacity: 1; }
+    exit 100% { opacity: 0; }
+  }
+  @keyframes change-font-size {
+    exit 0% { font-size: 10px; }
+    exit 100% { font-size: 20px; }
+  }
+  #container {
+    width: 200px;
+    height: 200px;
+    overflow-y: scroll;
+    overflow-x: hidden;
+  }
+  .target {
+    width: 100px;
+    height: 100px;
+    background-color: red;
+  }
+  .content {
+    width: 400px;
+    height: 400px;
+    background-color: blue;
+  }
+</style>
+
+<body>
+<script>
+"use strict";
+
+setup(assert_implements_animation_timeline);
+
+const createTargetWithStuff = function(t, divClasses) {
+  let container = document.createElement('div');
+  container.id = 'container';
+  document.body.appendChild(container);
+
+  // *** When testing inset
+  // <div id='container'>
+  //   <div class='content'></div>
+  //   <div class='target'></div>
+  //   <div class='content'></div>
+  // </div>
+  // *** When testing axis
+  // <div id='container'>
+  //   <div class='target'></div>
+  //   <div class='content'></div>
+  // </div>
+
+  let divs = [];
+  let target;
+  for(let className of divClasses) {
+    let div = document.createElement('div');
+    div.className = className;
+    container.appendChild(div);
+
+    divs.push(div);
+    if(className === 'target')
+      target = div;
+  }
+
+  if (t && typeof t.add_cleanup === 'function') {
+    t.add_cleanup(() => {
+      for(let div of divs)
+        div.remove();
+      container.remove();
+    });
+  }
+
+  return [container, target];
+};
+
+async function scrollLeft(element, value) {
+  element.scrollLeft = value;
+  await waitForNextFrame();
+}
+
+async function scrollTop(element, value) {
+  element.scrollTop = value;
+  await waitForNextFrame();
+}
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, ['content', 'target', 'content']);
+  div.style.animation = "fade-in-out 1s linear";
+  div.style.animationTimeline = "view()";
+
+  await scrollTop(container, 200);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At enter 0%');
+  await scrollTop(container, 250);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At enter 50%');
+  await scrollTop(container, 300);
+  assert_equals(getComputedStyle(div).opacity, '1', 'At enter 100%');
+
+  await scrollTop(container, 400);
+  assert_equals(getComputedStyle(div).opacity, '1', 'At exit 0%');
+  await scrollTop(container, 450);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50%');
+  await scrollTop(container, 500);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At exit 100%');
+}, 'animation-timeline: view()');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, ['content', 'target', 'content']);
+  div.style.animation = "fade-in-out 1s linear";
+  div.style.animationTimeline = "view(50px)";
+
+  await scrollTop(container, 250);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At enter 0%');
+  await scrollTop(container, 300);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At enter 50%');
+
+  await scrollTop(container, 350);
+  assert_equals(getComputedStyle(div).opacity, '1', 'At enter 100% & exit 0%');
+
+  await scrollTop(container, 400);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50%');
+  await scrollTop(container, 450);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At exit 100%');
+}, 'animation-timeline: view(50px)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, ['content', 'target', 'content']);
+  div.style.animation = "fade-in-out 1s linear";
+  div.style.animationTimeline = "view(auto 50px)";
+
+  await scrollTop(container, 250);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At enter 0%');
+  await scrollTop(container, 300);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At enter 50%');
+  await scrollTop(container, 350);
+  assert_equals(getComputedStyle(div).opacity, '1', 'At enter 100%');
+
+  await scrollTop(container, 400);
+  assert_equals(getComputedStyle(div).opacity, '1', 'At exit 0%');
+  await scrollTop(container, 450);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50%');
+  await scrollTop(container, 500);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At exit 100%');
+}, 'animation-timeline: view(auto 50px)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, ['target', 'content']);
+  container.style.overflow = 'scroll';
+  div.style.animation = "fade-out 1s linear";
+  div.style.animationTimeline = "view(inline)";
+
+  await scrollLeft(container, 0);
+  assert_equals(getComputedStyle(div).opacity, '1', 'At exit 0%');
+  await scrollLeft(container, 50);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50%');
+  await scrollLeft(container, 100);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At exit 100%');
+}, 'animation-timeline: view(inline)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, ['target', 'content']);
+  container.style.overflow = 'scroll';
+  div.style.animation = "fade-out 1s linear";
+  div.style.animationTimeline = "view(horizontal)";
+
+  await scrollLeft(container, 0);
+  assert_equals(getComputedStyle(div).opacity, '1', 'At exit 0%');
+  await scrollLeft(container, 50);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50%');
+  await scrollLeft(container, 100);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At exit 100%');
+}, 'animation-timeline: view(horizontal)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, ['target', 'content']);
+  container.style.overflow = 'scroll';
+  div.style.animation = "fade-out 1s linear";
+  div.style.animationTimeline = "view(vertical)";
+
+  await scrollTop(container, 0);
+  assert_equals(getComputedStyle(div).opacity, '1', 'At exit 0%');
+  await scrollTop(container, 50);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50%');
+  await scrollTop(container, 100);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At exit 100%');
+}, 'animation-timeline: view(vertical)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, ['target', 'content']);
+  container.style.overflowY = 'hidden';
+  container.style.overflowX = 'scroll';
+  div.style.animation = "fade-out 1s linear";
+  div.style.animationTimeline = "view(horizontal 50px)";
+
+  await scrollLeft(container, 0);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50%');
+  await scrollLeft(container, 50);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At exit 100%');
+}, 'animation-timeline: view(horizontal 50px)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, ['target', 'content']);
+  container.style.overflow = 'scroll';
+  div.style.animation = "fade-out 1s linear, change-font-size 1s linear";
+  div.style.animationTimeline = "view(), view(inline)";
+
+  await scrollLeft(container, 0);
+  assert_equals(getComputedStyle(div).fontSize, '10px', 'At exit 0% inline');
+  await scrollLeft(container, 50);
+  assert_equals(getComputedStyle(div).fontSize, '15px', 'At exit 50% inline');
+  await scrollLeft(container, 100);
+  assert_equals(getComputedStyle(div).fontSize, '20px', 'At exit 100% inline');
+
+  await scrollLeft(container, 0);
+
+  await scrollTop(container, 0);
+  assert_equals(getComputedStyle(div).opacity, '1', 'At exit 0% block');
+  await scrollTop(container, 50);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50% block');
+  await scrollTop(container, 100);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At exit 100% block');
+
+  await scrollLeft(container, 50);
+  await scrollTop(container, 50);
+  assert_equals(getComputedStyle(div).fontSize, '15px', 'At exit 50% inline');
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50% block');
+}, 'animation-timeline: view(), view(inline)');
+
+promise_test(async t => {
+  let [container, div] = createTargetWithStuff(t, ['target', 'content']);
+  container.style.overflowY = 'hidden';
+  container.style.overflowX = 'scroll';
+  div.style.animation = "fade-out 1s linear";
+
+  div.style.animationTimeline = "view(inline)";
+  await scrollLeft(container, 0);
+  assert_equals(getComputedStyle(div).opacity, '1', 'At exit 0%');
+  await scrollLeft(container, 50);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50%');
+  await scrollLeft(container, 100);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At exit 100%');
+
+  div.style.animationTimeline = "view(inline 50px)";
+  await scrollLeft(container, 0);
+  assert_equals(getComputedStyle(div).opacity, '0.5', 'At exit 50%');
+  await scrollLeft(container, 50);
+  assert_equals(getComputedStyle(div).opacity, '0', 'At exit 100%');
+}, 'animation-timeline: view(inline) changes to view(inline 50px)');
+
+</script>
+</body>
\ No newline at end of file
diff --git a/testing/web-platform/tests/scroll-animations/css/get-animations-inactive-timeline.html b/testing/web-platform/tests/scroll-animations/css/get-animations-inactive-timeline.html
new file mode 100644
index 0000000000..10bf00fbbc
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/get-animations-inactive-timeline.html
@@ -0,0 +1,87 @@
+<!DOCTYPE html>
+<html>
+<meta charset="utf-8">
+<title>getAnimations for scroll-linked animations</title>
+<link rel="help"
+ href="https://www.w3.org/TR/web-animations-1/#animation-effect-phases-and-states">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes slide {
+    from { transform: translateX(100px);  }
+    to   { transform: translateX(100px); }
+  }
+
+  #container {
+    border:  10px solid lightgray;
+    overflow-x: scroll;
+    height:  200px;
+    width: 200px;
+    scroll-timeline-name:  timeline;
+  }
+  #spacer {
+    height:  200vh;
+  }
+  #target {
+    background-color:  green;
+    height:  100px;
+    width:  100px;
+    animation:  slide 1s linear;
+    animation-timeline: timeline;
+  }
+</style>
+<body>
+  <div id="container">
+    <div id="spacer"></div>
+    <div id="target"></div>
+  </div>
+</body>
+<script type="text/javascript">
+  setup(assert_implements_animation_timeline);
+
+  promise_test(async t => {
+    // Newly created timeline is inactive,
+    let animations = document.getAnimations();
+    assert_equals(animations.length, 1,
+                  'Single running animation');
+    assert_true(animations[0].timeline instanceof ScrollTimeline,
+                'Animation associated with a scroll timeline');
+    assert_equals(animations[0].timeline.currentTime, null,
+                  'Timeline is initially inactive');
+
+    // Canceled animation is no longer current.
+    const anim = animations[0];
+    animations[0].cancel();
+
+    assert_equals(
+        document.getAnimations().length, 0,
+        'A canceled animation is no longer returned by getAnimations');
+
+    // Replaying an animation makes it current.
+    anim.play();
+    assert_equals(
+        document.getAnimations().length, 1,
+        'A play-pending animation is return by getAnimations');
+
+    // Animation effect is still current even if the timeline's source element
+    // cannot be scrolled.
+    spacer.style = 'display: none';
+    t.add_cleanup(() => {
+      spacer.style = '';
+    });
+
+    animations = document.getAnimations();
+    assert_equals(
+        animations.length, 1,
+        'Running animation is included in getAnimations list even if ' +
+        'currentTime is null');
+    assert_true(animations[0].timeline  instanceof ScrollTimeline,
+                'Animation has timeline associated with an element that ' +
+                'cannot be scrolled');
+    assert_equals(animations[0].timeline.currentTime, null,
+                  'Inactive timeline when timeline\'s source element cannot ' +
+                  'be scrolled');
+  }, 'getAnimations includes inactive scroll-linked animations that have not ' +
+     'been canceled');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/named-range-keyframes-with-document-timeline.tentative.html b/testing/web-platform/tests/scroll-animations/css/named-range-keyframes-with-document-timeline.tentative.html
new file mode 100644
index 0000000000..a0094d3220
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/named-range-keyframes-with-document-timeline.tentative.html
@@ -0,0 +1,54 @@
+<!DOCTYPE html>
+<html>
+<meta charset="utf-8">
+<title>Named range keyframe offset when you have a document timeline</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes fade-in-animation {
+    from { opacity: 0 }
+
+    enter 0% { opacity: 0 }
+    enter 100% { opacity: 1 }
+    exit 0% { opacity: 1 }
+    exit 100% { opacity: 0 }
+
+    to { opacity: 1 }
+  }
+
+  #subject {
+    background-color: blue;
+    height: 200px;
+    width: 200px;
+    animation: linear both fade-in-animation;
+    animation-duration: 0.1s;
+    animation-play-state: paused;
+  }
+</style>
+<body onload="runTests()">
+  <div id="subject"></div>
+</body>
+
+<script type="text/javascript">
+  setup(assert_implements_animation_timeline);
+
+  function runTests() {
+    promise_test(async t => {
+      const anim = subject.getAnimations()[0];
+      anim.currentTime = -1;
+      assert_equals(getComputedStyle(subject).opacity, "0",
+              'unexpected value in the before phase');
+
+      anim.currentTime = 50;
+      assert_equals(getComputedStyle(subject).opacity, "0.5",
+              'unexpected value in the middle of the animation');
+
+      anim.currentTime = 100;
+      assert_equals(getComputedStyle(subject).opacity, "1",
+              'unexpected value in the after phase');
+    });
+  }
+</script>
+</html>
diff --git a/testing/web-platform/tests/scroll-animations/css/printing/animation-timeline-none-with-progress-print.tentative.html b/testing/web-platform/tests/scroll-animations/css/printing/animation-timeline-none-with-progress-print.tentative.html
new file mode 100644
index 0000000000..3939a1df48
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/printing/animation-timeline-none-with-progress-print.tentative.html
@@ -0,0 +1,56 @@
+<!DOCTYPE HTML>
+<html class="reftest-wait">
+<title>The animation-timeline:none with preserved progress for print</title>
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<meta name="assert" content="print correctly for an animation with animation-timeline:none with preserved progress">
+<link rel="match" href="animation-timeline-none-with-progress-ref.html">
+
+<style>
+  @keyframes anim {
+    from { transform: translateX(0px); }
+    to { transform: translateX(100px); }
+  }
+
+  #scroller {
+    scroll-timeline: timeline;
+    overflow: scroll;
+    width: 100px;
+    height: 100px;
+    scrollbar-width: none;
+  }
+
+  #contents {
+    height: 200px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    animation: anim 1s linear timeline;
+  }
+</style>
+
+<div id="scroller">
+  <div id="contents"></div>
+</div>
+<div id="box"></div>
+
+<script>
+  window.addEventListener('load', function() {
+    const scroller = document.getElementById("scroller");
+    // Move the scroller to the halfway point.
+    const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+    scroller.scrollTop = 0.5 * maxScroll;
+
+    window.requestAnimationFrame(() => {
+      let box = document.getElementById("box");
+      box.style.animationTimeline = "none";
+      getComputedStyle(box).marginLeft;
+
+      window.requestAnimationFrame(() => {
+        document.documentElement.classList.remove("reftest-wait");
+      });
+    });
+  });
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/printing/animation-timeline-none-with-progress-ref.html b/testing/web-platform/tests/scroll-animations/css/printing/animation-timeline-none-with-progress-ref.html
new file mode 100644
index 0000000000..09bcba2fd4
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/printing/animation-timeline-none-with-progress-ref.html
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<title>Reference for none animation-timeline</title>
+<style>
+  #scroller {
+    overflow: scroll;
+    width: 100px;
+    height: 100px;
+    scrollbar-width: none;
+  }
+
+  #contents {
+    height: 200px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    transform: translateX(50px);
+  }
+</style>
+
+<div id="scroller">
+  <div id="contents"></div>
+</div>
+<div id="box"></div>
+
+<script>
+  window.addEventListener('load', function() {
+    const scroller = document.getElementById("scroller");
+    // Move the scroller to the halfway point.
+    const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+    scroller.scrollTop = 0.5 * maxScroll;
+
+    document.documentElement.classList.remove("reftest-wait");
+  });
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-default-iframe-print.html b/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-default-iframe-print.html
new file mode 100644
index 0000000000..d732ca141a
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-default-iframe-print.html
@@ -0,0 +1,65 @@
+<!DOCTYPE HTML>
+<html class="reftest-wait">
+<title>The default scroll() timeline in the iframe for print</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<meta name="assert" content="CSS animation correctly updates values when using the default scroll() timeline">
+<link rel="match" href="../scroll-timeline-default-iframe-ref.html">
+<meta name="fuzzy" content="25;100">
+
+<iframe id="target" width="400" height="400" srcdoc='
+  <html>
+  <style>
+    @keyframes update {
+      from { transform: translateY(0px); }
+      to { transform: translateY(200px); }
+    }
+    html {
+      min-height: 100%;
+      padding-bottom: 100px;
+    }
+    #box {
+      width: 100px;
+      height: 100px;
+      background-color: green;
+      animation: update 1s linear;
+      animation-timeline: scroll();
+    }
+    #covered {
+      width: 100px;
+      height: 100px;
+      background-color: red;
+    }
+
+    * {
+      margin-top: 0px;
+      margin-bottom: 0px;
+    }
+  </style>
+  <script>
+    window.addEventListener("load", function() {
+      const scroller = document.scrollingElement;
+
+      // Move the scroller to the halfway point.
+      const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+      scroller.scrollTop = 0.5 * maxScroll;
+
+      window.requestAnimationFrame(() => {
+        window.parent.postMessage("ready", "*");
+      });
+    });
+  </script>
+  <body>
+    <div id="box"></div>
+    <div id="covered"></div>
+  </body>
+  </html>
+'></iframe>
+
+<script>
+  window.addEventListener("message", event => {
+    if (event.data == "ready") {
+      document.documentElement.classList.remove("reftest-wait");
+    }
+  }, false);
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-default-print.tentative.html b/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-default-print.tentative.html
new file mode 100644
index 0000000000..975a59812e
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-default-print.tentative.html
@@ -0,0 +1,62 @@
+<!DOCTYPE HTML>
+<html class="reftest-wait">
+<title>The default scroll() timeline for print</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<meta name="assert" content="CSS animation correctly updates values when using the default scroll() timeline">
+<link rel="match" href="../scroll-timeline-default-ref.html">
+
+<style>
+  @keyframes update {
+    from { transform: translateY(0px); }
+    to { transform: translateY(200px); }
+  }
+
+  html {
+    min-height: 100%;
+    padding-bottom: 100px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    animation: update 1s linear;
+    animation-timeline: scroll();
+  }
+
+  #covered {
+    width: 100px;
+    height: 100px;
+    background-color: red;
+  }
+
+  * {
+    margin-top: 0px;
+    margin-bottom: 0px;
+  }
+</style>
+
+<div id="box"></div>
+<div id="covered"></div>
+<script src="/web-animations/testcommon.js"></script>
+<script>
+  document.documentElement.addEventListener('TestRendered', async () => {
+    runTest();
+  }, { once: true });
+
+  async function runTest() {
+    const scroller = document.scrollingElement;
+
+    await waitForCompositorReady();
+
+    // Move the scroller to the halfway point.
+    const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+    scroller.scrollTop = 0.5 * maxScroll;
+
+    await waitForNextFrame();
+    await waitForNextFrame();
+
+    document.documentElement.classList.remove("reftest-wait");
+  }
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-specified-scroller-print.html b/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-specified-scroller-print.html
new file mode 100644
index 0000000000..7e5b6607b6
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-specified-scroller-print.html
@@ -0,0 +1,58 @@
+<!DOCTYPE HTML>
+<html class="reftest-wait">
+<title>A scroll timeline with a specified scroller for print</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-timelines">
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<meta name="assert" content="CSS animation correctly updates values when using a specified scroller">
+<link rel="match" href="scroll-timeline-specified-scroller-ref.html">
+
+<style>
+  @keyframes anim {
+    from { transform: translateX(0px); }
+    to { transform: translateX(100px); }
+  }
+
+  #scroller {
+    scroll-timeline: timeline;
+    overflow: scroll;
+    width: 100px;
+    height: 100px;
+    scrollbar-width: none;
+  }
+
+  #contents {
+    height: 200px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    animation: anim 1s linear;
+    animation-timeline: timeline;
+  }
+
+  @supports not (animation-timeline:timeline) {
+    #box {
+      animation-play-state: paused;
+    }
+  }
+</style>
+
+<div id="scroller">
+  <div id="contents"></div>
+</div>
+<div id="box"></div>
+
+<script>
+  window.addEventListener('load', function() {
+    const scroller = document.getElementById("scroller");
+    // Move the scroller to the halfway point.
+    const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+    scroller.scrollTop = 0.5 * maxScroll;
+
+    window.requestAnimationFrame(() => {
+      document.documentElement.classList.remove("reftest-wait");
+    });
+  });
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-specified-scroller-ref.html b/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-specified-scroller-ref.html
new file mode 100644
index 0000000000..9074f2454b
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/printing/scroll-timeline-specified-scroller-ref.html
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<title>Reference for scroll timeline with a specified scroller</title>
+<style>
+  #scroller {
+    overflow: scroll;
+    width: 100px;
+    height: 100px;
+    scrollbar-width: none;
+  }
+
+  #contents {
+    height: 200px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    transform: translateX(50px);
+  }
+</style>
+
+<div id="scroller">
+  <div id="contents"></div>
+</div>
+<div id="box"></div>
+
+<script>
+  window.addEventListener('load', function() {
+    const scroller = document.getElementById("scroller");
+    // Move the scroller to the halfway point.
+    const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+    scroller.scrollTop = 0.5 * maxScroll;
+
+    document.documentElement.classList.remove("reftest-wait");
+  });
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/progress-based-animation-animation-longhand-properties.tentative.html b/testing/web-platform/tests/scroll-animations/css/progress-based-animation-animation-longhand-properties.tentative.html
new file mode 100644
index 0000000000..f4f9a669f3
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/progress-based-animation-animation-longhand-properties.tentative.html
@@ -0,0 +1,255 @@
+<!DOCTYPE html>
+<title>The various animation longhands with progress based animations</title>
+<link rel="help" src="https://drafts.csswg.org/css-animations-2">
+<link rel="help" src="https://github.com/w3c/csswg-drafts/issues/4862">
+<link rel="help" src="https://github.com/w3c/csswg-drafts/issues/6674">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { translate: 0px; }
+    to { translate: 100px; }
+  }
+  #container {
+    width: 300px;
+    height: 300px;
+    overflow: scroll;
+  }
+  #target {
+    width: 100px;
+    height: 100px;
+    translate: none;
+  }
+</style>
+<body>
+<div id="log"></div>
+<script>
+"use strict";
+
+setup(assert_implements_animation_timeline);
+
+const createTargetAndScroller = function(t) {
+  let container = document.createElement('div');
+  container.id = 'container';
+  let target = document.createElement('div');
+  target.id = 'target';
+  let content = document.createElement('div');
+  content.style.blockSize = '100%';
+
+  // The height of target is 100px and the content is 100%, so the scroll range
+  // is [0, 100].
+
+  // <div id='container'>
+  //   <div id='target'></div>
+  //   <div style='block-size: 100%;'></div>
+  // </div>
+  document.body.appendChild(container);
+  container.appendChild(target);
+  container.appendChild(content);
+
+  if (t && typeof t.add_cleanup === 'function') {
+    t.add_cleanup(() => {
+      content.remove();
+      target.remove();
+      container.remove();
+    });
+  }
+
+  return [target, container];
+};
+
+async function scrollTop(element, value) {
+  element.scrollTop = value;
+  await waitForNextFrame();
+}
+
+// ------------------------------
+// Test animation-duration
+// ------------------------------
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim';
+  target.style.animationTimeline = 'scroll(nearest)';
+
+  await scrollTop(scroller, 25); // [0, 100].
+  assert_equals(getComputedStyle(target).translate, '25px');
+}, 'animation-duration');
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '0s linear anim forwards';
+  target.style.animationTimeline = 'scroll(nearest)';
+
+  await scrollTop(scroller, 25); // [0, 100].
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, 'animation-duration: 0s');
+
+
+// ------------------------------
+// Test animation-iteration-count
+// ------------------------------
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim';
+  target.style.animationTimeline = 'scroll(nearest)';
+
+  await scrollTop(scroller, 25); // [0, 100].
+  assert_equals(getComputedStyle(target).translate, '25px');
+
+  // Let animation become 50% in the 1st iteration.
+  target.style.animationIterationCount = '2';
+  await waitForCSSScrollTimelineStyle();
+  assert_equals(getComputedStyle(target).translate, '50px');
+
+  // Let animation become 0% in the 2nd iteration.
+  target.style.animationIterationCount = '4';
+  await waitForCSSScrollTimelineStyle();
+  assert_equals(getComputedStyle(target).translate, '0px');
+}, 'animation-iteration-count');
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim forwards';
+  target.style.animationTimeline = 'scroll(nearest)';
+  target.style.animationIterationCount = '0';
+
+  await scrollTop(scroller, 25); // [0, 100].
+  assert_equals(getComputedStyle(target).translate, '0px');
+}, 'animation-iteration-count: 0');
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim forwards';
+  target.style.animationTimeline = 'scroll(nearest)';
+  target.style.animationIterationCount = 'infinite';
+
+  await scrollTop(scroller, 25); // [0, 100].
+  assert_equals(getComputedStyle(target).translate, '100px');
+}, 'animation-iteration-count: infinite');
+
+
+// ------------------------------
+// Test animation-direction
+// ------------------------------
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim';
+  target.style.animationTimeline = 'scroll(nearest)';
+
+  await scrollTop(scroller, 25) // [0, 100].
+  assert_equals(getComputedStyle(target).translate, '25px');
+}, 'animation-direction: normal');
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim';
+  target.style.animationTimeline = 'scroll(nearest)';
+  target.style.animationDirection = 'reverse';
+
+  await scrollTop(scroller, 25); // 25% in the reversing direction.
+  assert_equals(getComputedStyle(target).translate, '75px');
+}, 'animation-direction: reverse');
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim';
+  target.style.animationTimeline = 'scroll(nearest)';
+  target.style.animationIterationCount = '2';
+  target.style.animationDirection = 'alternate';
+
+  await scrollTop(scroller, 10); // 20% in the 1st iteration.
+  assert_equals(getComputedStyle(target).translate, '20px');
+
+  await scrollTop(scroller, 60); // 20% in the 2nd iteration (reversing direction).
+  assert_equals(getComputedStyle(target).translate, '80px');
+}, 'animation-direction: alternate');
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim';
+  target.style.animationTimeline = 'scroll(nearest)';
+  target.style.animationIterationCount = '2';
+  target.style.animationDirection = 'alternate-reverse';
+
+  await scrollTop(scroller, 10); // 20% in the 1st iteration (reversing direction).
+  assert_equals(getComputedStyle(target).translate, '80px');
+
+  await scrollTop(scroller, 60); // 20% in the 2nd iteration.
+  assert_equals(getComputedStyle(target).translate, '20px');
+}, 'animation-direction: alternate-reverse');
+
+
+// ------------------------------
+// Test animation-delay
+// ------------------------------
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim';
+  target.style.animationTimeline = 'scroll(nearest)';
+
+  await scrollTop(scroller, 25); // [0, 100].
+  assert_equals(getComputedStyle(target).translate, '25px');
+
+  //    (start delay: 10s)    (duration: 10s)
+  //         before              active
+  // |--------------------|--------------------|
+  // 0px                 50px                100px (The scroller)
+  //                      0%                 100%  (The iteration progress)
+
+  // Let animation be in before phase.
+  target.style.animationDelay = '10s';
+  target.style.animationDelayStart = '10s'; // crbug.com/1375994
+  assert_equals(getComputedStyle(target).translate, 'none');
+
+  await scrollTop(scroller, 50); // The animation enters active phase.
+  assert_equals(getComputedStyle(target).translate, '0px');
+
+  await scrollTop(scroller, 75); // The ieration progress is 50%.
+  assert_equals(getComputedStyle(target).translate, '50px');
+}, 'animation-delay with a positive value');
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim';
+  target.style.animationTimeline = 'scroll(nearest)';
+
+  //         active
+  // |--------------------|
+  // 0px                100px (The scroller)
+  // 50%                100%  (The iteration progress)
+
+  await scrollTop(scroller, 20); // [0, 100].
+  target.style.animationDelay = '-5s';
+  target.style.animationDelayStart = '-5s'; // crbug.com/1375994
+  await waitForCSSScrollTimelineStyle();
+  assert_equals(getComputedStyle(target).translate, '60px');
+}, 'animation-delay with a negative value');
+
+
+// ------------------------------
+// Test animation-fill-mode
+// ------------------------------
+
+promise_test(async t => {
+  let [target, scroller] = createTargetAndScroller(t);
+  target.style.animation = '10s linear anim';
+  target.style.animationTimeline = 'scroll(nearest)';
+  target.style.animationDelay = '10s';
+  target.style.animationDelayStart = '10s'; // crbug.com/1375994
+
+  await scrollTop(scroller, 25);
+  assert_equals(getComputedStyle(target).translate, 'none');
+
+  target.style.animationFillMode = 'backwards';
+  await waitForCSSScrollTimelineStyle();
+  assert_equals(getComputedStyle(target).translate, '0px');
+}, 'animation-fill-mode');
+
+</script>
+</body>
diff --git a/testing/web-platform/tests/scroll-animations/css/progress-based-animation-timeline.html b/testing/web-platform/tests/scroll-animations/css/progress-based-animation-timeline.html
new file mode 100644
index 0000000000..2e910cbe51
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/progress-based-animation-timeline.html
@@ -0,0 +1,52 @@
+<!DOCTYPE html>
+<title>CSS Animation using progress based timeline</title>
+<link rel="help" src="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<style>
+  main > div {
+    overflow: hidden;
+    width: 100px;
+    height: 100px;
+  }
+  main > div > div {
+    height: 200px;
+  }
+
+  @keyframes top {
+    from { top: 100px; }
+    to { top: 200px; }
+  }
+
+  #scroller1 {
+    scroll-timeline: top_timeline;
+  }
+
+  #element {
+    animation-name: top;
+    animation-duration: 10s;
+    animation-timing-function: linear;
+    animation-timeline: top_timeline;
+  }
+  /* Ensure stable expectations if feature is not supported */
+  @supports not (animation-timeline:foo) {
+    #element { animation-play-state: paused; }
+  }
+</style>
+<main>
+  <div id=scroller1><div></div></div>
+  <div id=element></div>
+</main>
+<script>
+  window.onload = async () => {
+    promise_test(async (t) => {
+      await waitForNextFrame();
+      const anim = document.getAnimations()[0];
+      await anim.ready;
+      scroller1.scrollTop = 20;
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(element).top, '120px');
+    }, 'progress based animation timeline works');
+  };
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-computed.tentative.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-computed.tentative.html
new file mode 100644
index 0000000000..8e23968b8e
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-computed.tentative.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/6674">
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/rewrite#scroll-timeline-axis">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+</head>
+<style>
+  #outer { scroll-timeline-axis: inline; }
+  #target { scroll-timeline-axis: vertical; }
+</style>
+<div id="outer">
+  <div id="target"></div>
+</div>
+<script>
+test_computed_value('scroll-timeline-axis', 'initial', 'block');
+test_computed_value('scroll-timeline-axis', 'inherit', 'inline');
+test_computed_value('scroll-timeline-axis', 'unset', 'block');
+test_computed_value('scroll-timeline-axis', 'revert', 'block');
+test_computed_value('scroll-timeline-axis', 'block');
+test_computed_value('scroll-timeline-axis', 'inline');
+test_computed_value('scroll-timeline-axis', 'vertical');
+test_computed_value('scroll-timeline-axis', 'horizontal');
+
+test(() => {
+  let style = getComputedStyle(document.getElementById('target'));
+  assert_not_equals(Array.from(style).indexOf('scroll-timeline-axis'), -1);
+}, 'The scroll-timeline-axis property shows up in CSSStyleDeclaration enumeration');
+
+test(() => {
+  let style = document.getElementById('target').style;
+  assert_not_equals(style.cssText.indexOf('scroll-timeline-axis'), -1);
+}, 'The scroll-timeline-axis property shows up in CSSStyleDeclaration.cssText');
+
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-parsing.tentative.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-parsing.tentative.html
new file mode 100644
index 0000000000..81be07e38f
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-parsing.tentative.html
@@ -0,0 +1,27 @@
+<!DOCTYPE html>
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/6674">
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/rewrite#scroll-timeline-axis">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+</head>
+<div id="target"></div>
+
+<script>
+
+test_valid_value('scroll-timeline-axis', 'initial');
+test_valid_value('scroll-timeline-axis', 'inherit');
+test_valid_value('scroll-timeline-axis', 'unset');
+test_valid_value('scroll-timeline-axis', 'revert');
+
+test_valid_value('scroll-timeline-axis', 'block');
+test_valid_value('scroll-timeline-axis', 'inline');
+test_valid_value('scroll-timeline-axis', 'vertical');
+test_valid_value('scroll-timeline-axis', 'horizontal');
+
+test_invalid_value('scroll-timeline-axis', 'abc');
+test_invalid_value('scroll-timeline-axis', '10px');
+test_invalid_value('scroll-timeline-axis', 'auto');
+test_invalid_value('scroll-timeline-axis', 'none');
+
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-writing-mode.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-writing-mode.html
new file mode 100644
index 0000000000..90912bfc22
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-axis-writing-mode.html
@@ -0,0 +1,126 @@
+<!DOCTYPE html>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#scroll-timeline-axis">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<style>
+  .scroller {
+    overflow: hidden;
+    width: 100px;
+    height: 100px;
+  }
+  .contents {
+    height: 200px;
+    width: 200px;
+  }
+  @keyframes expand {
+    from { width: 100px; }
+    to { width: 200px; }
+  }
+  #timeline_initial_axis {
+    scroll-timeline: timeline_initial_axis;
+  }
+  #timeline_vertical {
+    scroll-timeline: vertical timeline_vertical;
+  }
+  #timeline_horizontal {
+    scroll-timeline: horizontal timeline_horizontal;
+  }
+  #timeline_block_in_horizontal {
+    scroll-timeline: block timeline_block_in_horizontal;
+  }
+  #timeline_inline_in_horizontal {
+    scroll-timeline: inline timeline_inline_in_horizontal;
+  }
+  #timeline_block_in_vertical {
+    scroll-timeline: block timeline_block_in_vertical;
+    writing-mode: vertical-lr;
+  }
+  #timeline_inline_in_vertical {
+    scroll-timeline: inline timeline_inline_in_vertical;
+    writing-mode: vertical-lr;
+  }
+  #container > div {
+    width: 0px;
+    animation-name: expand;
+    animation-duration: 10s;
+    animation-timing-function: linear;
+  }
+  /* Ensure stable expectations if feature is not supported */
+  @supports not (animation-timeline:foo) {
+    #container > div { animation-play-state: paused; }
+  }
+  #element_initial_axis { animation-timeline: timeline_initial_axis; }
+  #element_vertical { animation-timeline: timeline_vertical; }
+  #element_horizontal { animation-timeline: timeline_horizontal; }
+  #element_block_in_horizontal { animation-timeline: timeline_block_in_horizontal; }
+  #element_inline_in_horizontal { animation-timeline: timeline_inline_in_horizontal; }
+  #element_block_in_vertical { animation-timeline: timeline_block_in_vertical; }
+  #element_inline_in_vertical { animation-timeline: timeline_inline_in_vertical; }
+</style>
+<div class=scroller id=timeline_initial_axis><div class=contents></div></div>
+<div class=scroller id=timeline_vertical><div class=contents></div></div>
+<div class=scroller id=timeline_horizontal><div class=contents></div></div>
+<div class=scroller id=timeline_block_in_horizontal><div class=contents></div></div>
+<div class=scroller id=timeline_inline_in_horizontal><div class=contents></div></div>
+<div class=scroller id=timeline_block_in_vertical><div class=contents></div></div>
+<div class=scroller id=timeline_inline_in_vertical><div class=contents></div></div>
+<div id=container>
+  <div id=element_initial_axis></div>
+  <div id=element_vertical></div>
+  <div id=element_horizontal></div>
+  <div id=element_block_in_horizontal></div>
+  <div id=element_inline_in_horizontal></div>
+  <div id=element_block_in_vertical></div>
+  <div id=element_inline_in_vertical></div>
+</div>
+<script>
+  // Animations linked to vertical scroll-timelines are at 75% progress.
+  timeline_initial_axis.scrollTop = 75;
+  timeline_vertical.scrollTop = 75;
+  timeline_block_in_horizontal.scrollTop = 75;
+  timeline_inline_in_vertical.scrollTop = 75;
+  // Animations linked to horizontal scroll-timelines are at 25% progress.
+  timeline_horizontal.scrollLeft = 25;
+  timeline_block_in_vertical.scrollLeft = 25;
+  timeline_inline_in_horizontal.scrollLeft = 25;
+
+  promise_test(async (t) => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element_initial_axis).width, '175px');
+  }, 'Initial axis');
+
+  promise_test(async (t) => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element_vertical).width, '175px');
+  }, 'Vertical axis');
+
+  promise_test(async (t) => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element_horizontal).width, '125px');
+  }, 'Horizontal axis');
+
+  promise_test(async (t) => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element_block_in_horizontal).width, '175px');
+  }, 'Block axis in horizontal writing-mode');
+
+  promise_test(async (t) => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element_inline_in_horizontal).width, '125px');
+  }, 'Inline axis in horizontal writing-mode');
+
+  promise_test(async (t) => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(timeline_block_in_vertical).writingMode, 'vertical-lr');
+    assert_equals(getComputedStyle(element_block_in_vertical).width, '125px');
+  }, 'Block axis in vertical writing-mode');
+
+  promise_test(async (t) => {
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(timeline_inline_in_vertical).writingMode, 'vertical-lr');
+    assert_equals(getComputedStyle(element_inline_in_vertical).width, '175px');
+  }, 'Inline axis in vertical writing-mode');
+
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-iframe-ref.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-iframe-ref.html
new file mode 100644
index 0000000000..1ab5646c8b
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-iframe-ref.html
@@ -0,0 +1,33 @@
+<!DOCTYPE html>
+<title>Reference for default scroll() timeline</title>
+<iframe width="400" height="400" srcdoc='
+  <html>
+  <style>
+    html {
+      min-height: 100%;
+      padding-bottom: 100px;
+    }
+
+    #box {
+      width: 100px;
+      height: 100px;
+      background-color: green;
+      transform: translateY(100px);
+    }
+
+    * {
+      margin-top: 0px;
+      margin-bottom: 0px;
+    }
+  </style>
+  <script>
+    window.addEventListener("load", function() {
+      // Move the scroller to halfway.
+      const scroller = document.scrollingElement;
+      const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+      scroller.scrollTop = 0.5 * maxScroll;
+    });
+  </script>
+  <div id="box"></div>
+  </html>
+'></iframe>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-iframe.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-iframe.html
new file mode 100644
index 0000000000..dbcf5941a8
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-iframe.html
@@ -0,0 +1,73 @@
+<!DOCTYPE HTML>
+<html class="reftest-wait">
+<title>The default scroll() timeline in the iframe</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<meta name="assert" content="CSS animation correctly updates values when using the default scroll() timeline">
+<link rel="match" href="scroll-timeline-default-iframe-ref.html">
+
+<iframe id="target" width="400" height="400" srcdoc='
+  <html>
+  <style>
+    @keyframes update {
+      from { transform: translateY(0px); }
+      to { transform: translateY(200px); }
+    }
+    html {
+      min-height: 100%;
+      padding-bottom: 100px;
+    }
+    #box {
+      width: 100px;
+      height: 100px;
+      background-color: green;
+      animation: update 1s linear;
+      animation-timeline: scroll();
+    }
+    #covered {
+      width: 100px;
+      height: 100px;
+      background-color: red;
+    }
+
+    * {
+      margin-top: 0px;
+      margin-bottom: 0px;
+    }
+  </style>
+  <script src="/web-animations/testcommon.js"></script>
+  <script>
+    window.addEventListener("load", async function() {
+      const scroller = document.scrollingElement;
+
+      // Move the scroller to the halfway point.
+      const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+      scroller.scrollTop = 0.5 * maxScroll;
+
+      await waitForCompositorReady();
+      await waitForNextFrame();
+      await waitForNextFrame();
+
+      window.parent.postMessage("success", "*");
+    });
+  </script>
+  <body>
+    <div id="box"></div>
+    <div id="covered"></div>
+  </body>
+  </html>
+'></iframe>
+<script src="/web-animations/testcommon.js"></script>
+<script>
+  async function finishTest() {
+    await waitForCompositorReady();
+    await waitForNextFrame();
+    await waitForNextFrame();
+    document.documentElement.classList.remove("reftest-wait");
+  }
+  window.addEventListener("message", event => {
+    if (event.data == "success") {
+      finishTest();
+    }
+  }, false);
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-quirks-mode.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-quirks-mode.html
new file mode 100644
index 0000000000..d2c28d86b6
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-quirks-mode.html
@@ -0,0 +1,63 @@
+<html class="reftest-wait">
+<title>The default scroll() timeline in quirks mode</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<meta name="assert" content="CSS animation correctly updates values when using the default scroll() timeline">
+<link rel="match" href="scroll-timeline-default-ref.html">
+
+<style>
+  @keyframes update {
+    from { transform: translateY(0px); }
+    to { transform: translateY(200px); }
+  }
+
+  html {
+    min-height: 100%;
+    padding-bottom: 100px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    animation: update 1s linear;
+    animation-timeline: scroll();
+  }
+
+  #covered {
+    width: 100px;
+    height: 100px;
+    background-color: red;
+  }
+
+  * {
+    margin-top: 0px;
+    margin-bottom: 0px;
+  }
+</style>
+
+<div id="box"></div>
+<div id="covered"></div>
+<script src="/web-animations/testcommon.js"></script>
+<script>
+document.documentElement.addEventListener('TestRendered', async () => {
+  runTest();
+}, { once: true });
+
+async function runTest() {
+  const scroller = document.scrollingElement;
+
+  await waitForCompositorReady();
+
+  // Move the scroller to the halfway point. Then advance to the next frame
+  // to pick up the new timeline time.
+  const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+  scroller.scrollTop = 0.5 * maxScroll;
+
+  await waitForNextFrame();
+  await waitForNextFrame();
+
+  document.documentElement.classList.remove("reftest-wait");
+}
+
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-ref.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-ref.html
new file mode 100644
index 0000000000..cb3b60e4bd
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-ref.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<title>Reference for default scroll() timeline</title>
+<style>
+  html {
+    min-height: 100%;
+    padding-bottom: 100px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    transform: translateY(100px);
+  }
+
+  * {
+    margin-top: 0px;
+    margin-bottom: 0px;
+  }
+</style>
+
+<div id="box"></div>
+
+<script>
+  window.addEventListener('load', function() {
+    // Move the scroller to halfway.
+    const scroller = document.scrollingElement;
+    const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+    scroller.scrollTop = 0.5 * maxScroll;
+  });
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-writing-mode-rl-ref.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-writing-mode-rl-ref.html
new file mode 100644
index 0000000000..3c072829e6
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-writing-mode-rl-ref.html
@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<title>Reference for default scroll() timeline with vertical-rl</title>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<style>
+  html {
+    min-block-size: 100%;
+    padding-block-end: 100px;
+    writing-mode: vertical-rl
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    transform: translateX(-100px);
+  }
+
+  * {
+    margin-block: 0px;
+  }
+</style>
+
+<div id="box"></div>
+
+<script>
+  window.addEventListener('load', function() {
+    // Move the scroller to halfway.
+    const scroller = document.scrollingElement;
+    const maxScroll = scroller.scrollWidth - scroller.clientWidth;
+    scroller.scrollLeft = -0.5 * maxScroll;
+  });
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-writing-mode-rl.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-writing-mode-rl.html
new file mode 100644
index 0000000000..27e6ec196b
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default-writing-mode-rl.html
@@ -0,0 +1,65 @@
+<!DOCTYPE HTML>
+<html class="reftest-wait">
+<title>The default scroll() timeline with writing-mode:vertical-rl</title>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<meta name="assert" content="CSS animation correctly updates values when using
+                             the default scroll() timeline with writing-mode:vertical-rl">
+<link rel="match" href="scroll-timeline-default-writing-mode-rl-ref.html">
+
+<style>
+  @keyframes update {
+    from { transform: translateX(0px); }
+    to { transform: translateX(-200px); }
+  }
+
+  html {
+    min-block-size: 100%;
+    padding-block-end: 100px;
+    writing-mode: vertical-rl;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    animation: update 1s linear;
+    animation-timeline: scroll();
+  }
+
+  #covered {
+    width: 100px;
+    height: 100px;
+    background-color: red;
+  }
+
+  * {
+    margin-block: 0px;
+  }
+</style>
+
+<div id="box"></div>
+<div id="covered"></div>
+
+<script src="/web-animations/testcommon.js"></script>
+<script>
+  document.documentElement.addEventListener('TestRendered', async () => {
+    runTest();
+  }, { once: true });
+
+  async function runTest() {
+    const scroller = document.scrollingElement;
+
+    await waitForCompositorReady();
+
+    // Move the scroller to the halfway point.
+    const maxScroll = scroller.scrollWidth - scroller.clientWidth;
+    scroller.scrollLeft = -0.5 * maxScroll;
+
+    await waitForNextFrame();
+    await waitForNextFrame();
+
+    document.documentElement.classList.remove("reftest-wait");
+  }
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default.html
new file mode 100644
index 0000000000..07eda33fd0
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-default.html
@@ -0,0 +1,63 @@
+<!DOCTYPE HTML>
+<html class="reftest-wait">
+<title>The default scroll() timeline</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<meta name="assert" content="CSS animation correctly updates values when using the default scroll() timeline">
+<link rel="match" href="scroll-timeline-default-ref.html">
+
+<style>
+  @keyframes update {
+    from { transform: translateY(0px); }
+    to { transform: translateY(200px); }
+  }
+
+  html {
+    min-height: 100%;
+    padding-bottom: 100px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    animation: update 1s linear;
+    animation-timeline: scroll();
+  }
+
+  #covered {
+    width: 100px;
+    height: 100px;
+    background-color: red;
+  }
+
+  * {
+    margin-top: 0px;
+    margin-bottom: 0px;
+  }
+</style>
+
+<div id="box"></div>
+<div id="covered"></div>
+
+<script src="/web-animations/testcommon.js"></script>
+<script>
+  document.documentElement.addEventListener('TestRendered', async () => {
+    runTest();
+  }, { once: true });
+
+  async function runTest() {
+    const scroller = document.scrollingElement;
+
+    await waitForCompositorReady();
+
+    // Move the scroller to the halfway point.
+    const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+    scroller.scrollTop = 0.5 * maxScroll;
+
+    await waitForNextFrame();
+    await waitForNextFrame();
+
+    document.documentElement.classList.remove("reftest-wait");
+  }
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-document-scroller-quirks.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-document-scroller-quirks.html
new file mode 100644
index 0000000000..809a658a15
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-document-scroller-quirks.html
@@ -0,0 +1,36 @@
+<!-- Quirks mode -->
+<title>Tests the document scroller in quirks mode</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://bugs.chromium.org/p/chromium/issues/detail?id=1180575">
+<link rel="author" href="mailto:andruud@chromium.org">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/scroll-animations/scroll-timelines/testcommon.js"></script>
+<script src="/css/css-animations/support/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { z-index: 100; }
+    to { z-index: 100; }
+  }
+  #element {
+    animation: anim forwards;
+    animation-timeline: scroll(root);
+  }
+  #spacer {
+    height:  200vh;
+  }
+</style>
+<div id=element></div>
+<div id=spacer></div>
+
+<script>
+'use strict';
+
+setup(assert_implements_animation_timeline);
+
+promise_test(async () => {
+  await waitForCSSScrollTimelineStyle();
+  assert_equals(getComputedStyle(element).zIndex, "100");
+});
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-dynamic.tentative.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-dynamic.tentative.html
new file mode 100644
index 0000000000..b0880a7cc5
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-dynamic.tentative.html
@@ -0,0 +1,267 @@
+<!DOCTYPE html>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#scroll-timelines">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  main > div {
+    overflow: hidden;
+    width: 100px;
+    height: 100px;
+  }
+  main > div > div {
+    height: 200px;
+  }
+  @keyframes expand {
+    from { width: 100px; }
+    to { width: 200px; }
+  }
+  #element {
+    width: 0px;
+    height: 20px;
+    animation-name: expand;
+    /* Some of the tests in this file assume animations attached to the
+       DocumentTimeline are "stopped" without actually being paused.
+       Using 600s + steps(10, end) achieves this for one minute.*/
+    animation-duration: 600s;
+    animation-timing-function: steps(10, end);
+  }
+</style>
+<main>
+  <div id=scroller1><div></div></div>
+  <div id=scroller2><div></div></div>
+  <div id=container></div>
+</main>
+<script>
+  // Force layout of scrollers.
+  scroller1.offsetTop;
+  scroller2.offsetTop;
+
+  // Note the steps(10, end) timing function and height:100px. (10px scroll
+  // resolution).
+  scroller1.scrollTop = 20;
+  scroller2.scrollTop = 40;
+
+  function insertElement() {
+    let element = document.createElement('div');
+    element.id = 'element';
+    container.append(element);
+    return element;
+  }
+
+  // Runs a test with dynamically added/removed elements or CSS rules.
+  // Each test is instantiated twice: once for the initial style resolve where
+  // the DOM change was effectuated, and once after scrolling.
+  function dynamic_rule_test(func, description) {
+    // assert_width is an async function which verifies that the computed value
+    // of 'width' is as expected.
+    const instantiate = (assert_width, description) => {
+      promise_test(async (t) => {
+        try {
+          await func(t, assert_width);
+        } finally {
+          while (container.firstChild)
+            container.firstChild.remove();
+          scroller1.style = '';
+          scroller2.style = '';
+        }
+      }, description);
+    };
+
+    // Verify that the computed style is as expected after a full frame update
+    // following the rule change took place.
+    instantiate(async (element, expected) => {
+      await waitForCSSScrollTimelineStyle();
+      assert_equals(getComputedStyle(element).width, expected);
+    }, description + ' [immediate]');
+
+    // Verify that the computed style after scrolling a bit.
+    instantiate(async (element, expected) => {
+      scroller1.scrollTop = scroller1.scrollTop + 10;
+      scroller2.scrollTop = scroller2.scrollTop + 10;
+      await waitForNextFrame();
+      scroller1.scrollTop = scroller1.scrollTop - 10;
+      scroller2.scrollTop = scroller2.scrollTop - 10;
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(element).width, expected);
+    }, description + ' [scroll]');
+  }
+
+  dynamic_rule_test(async (t, assert_width) => {
+    let element = insertElement();
+
+    // This element initially has a DocumentTimeline.
+    await assert_width(element, '100px');
+
+    // Switch to scroll timeline.
+    scroller1.style.scrollTimelineName = 'timeline';
+    element.style.animationTimeline = 'timeline';
+    await assert_width(element, '120px');
+
+    // Switching from ScrollTimeline -> DocumentTimeline should preserve
+    // current time.
+    scroller1.style = '';
+    element.style = '';
+    await assert_width(element, '120px');
+  }, 'Switching between document and scroll timelines');
+
+  dynamic_rule_test(async (t, assert_width) => {
+    let element = insertElement();
+
+    // Flush style and create the animation with play pending.
+    getComputedStyle(element).animation;
+
+    let anim = element.getAnimations()[0];
+    assert_true(anim.pending, "The animation is in play pending");
+
+    // Switch to scroll timeline for a pending animation.
+    scroller1.style.scrollTimelineName = 'timeline';
+    element.style.animationTimeline = 'timeline';
+
+    await anim.ready;
+    assert_false(anim.pending, "The animation is not pending");
+
+    await assert_width(element, '120px');
+  }, 'Switching pending animation from document to scroll timelines');
+
+  dynamic_rule_test(async (t, assert_width) => {
+    let element = insertElement();
+
+    // Note: #scroller1 is at 20%, and #scroller2 is at 40%.
+    scroller1.style.scrollTimelineName = 'timeline1';
+    scroller2.style.scrollTimelineName = 'timeline2';
+
+    await assert_width(element, '100px');
+
+    element.style.animationTimeline = 'timeline1';
+    await assert_width(element, '120px');
+
+    element.style.animationTimeline = 'timeline2';
+    await assert_width(element, '140px');
+
+    element.style.animationTimeline = 'timeline1';
+    await assert_width(element, '120px');
+
+    // Switching from ScrollTimeline -> DocumentTimeline should preserve
+    // current time.
+    element.style.animationTimeline = '';
+    await assert_width(element, '120px');
+
+  }, 'Changing computed value of animation-timeline changes effective timeline');
+
+  dynamic_rule_test(async (t, assert_width) => {
+    let element = insertElement();
+
+    scroller1.style.scrollTimelineName = 'timeline';
+
+    // DocumentTimeline applies by default.
+    await assert_width(element, '100px');
+
+    // DocumentTimeline -> none
+    element.style.animationTimeline = 'none';
+    await assert_width(element, '0px');
+
+    // none -> DocumentTimeline
+    element.style.animationTimeline = '';
+    await assert_width(element, '100px');
+
+    // DocumentTimeline -> ScrollTimeline
+    element.style.animationTimeline = 'timeline';
+    await assert_width(element, '120px');
+
+    // ScrollTimeline -> none
+    element.style.animationTimeline = 'none';
+    await assert_width(element, '120px');
+
+    // none -> ScrollTimeline
+    element.style.animationTimeline = 'timeline';
+    await assert_width(element, '120px');
+  }, 'Changing to/from animation-timeline:none');
+
+
+  dynamic_rule_test(async (t, assert_width) => {
+    let element = insertElement();
+
+    element.style.animationTimeline = 'timeline';
+
+    // Unknown animation-timeline, current time held at zero.
+    await assert_width(element, '100px');
+
+    scroller1.style.scrollTimelineName = 'timeline';
+    await assert_width(element, '120px');
+
+    scroller2.style.scrollTimelineName = 'timeline';
+    await assert_width(element, '140px');
+  }, 'Changing scroll-timeline on preceding elements affects target element');
+
+
+  dynamic_rule_test(async (t, assert_width) => {
+    let element = insertElement();
+
+    element.style.animationDirection = 'reverse';
+    element.style.animationTimeline = 'timeline';
+
+    // Unknown animation-timeline, current time held at zero.
+    await assert_width(element, '200px');
+
+    // Note: #scroller1 is at 20%.
+    scroller1.style.scrollTimelineName = 'timeline';
+    await assert_width(element, '180px');
+
+    // Note: #scroller2 is at 40%.
+    scroller2.style.scrollTimelineName = 'timeline';
+    await assert_width(element, '160px');
+
+    element.style.animationDirection = '';
+    await assert_width(element, '140px');
+  }, 'Reverse animation direction');
+
+  dynamic_rule_test(async (t, assert_width) => {
+    let element = insertElement();
+    element.style.animationTimeline = 'timeline';
+
+    // Unknown animation-timeline, current time held at zero.
+    await assert_width(element, '100px');
+
+    // Note: #scroller1 is at 20%.
+    scroller1.style.scrollTimelineName = 'timeline';
+    await assert_width(element, '120px');
+
+    element.style.animationPlayState = 'paused';
+
+    // We should still be at the same position after pausing.
+    await assert_width(element, '120px');
+
+    // Note: #scroller2 is at 40%.
+    scroller2.style.scrollTimelineName = 'timeline';
+
+    // Even when switching timelines, we should be at the same position until
+    // we unpause.
+    await assert_width(element, '120px');
+
+    // Unpausing should synchronize to the scroll position.
+    element.style.animationPlayState = '';
+    await assert_width(element, '140px');
+  }, 'Switching timelines while paused');
+
+  dynamic_rule_test(async (t, assert_width) => {
+    let element = insertElement();
+
+    // Note: #scroller1 is at 20%.
+    scroller1.style.scrollTimelineName = 'timeline';
+
+    await assert_width(element, '100px');
+
+    element.style.animationTimeline = 'timeline';
+    element.style.animationPlayState = 'paused';
+
+    // Pausing should happen before the timeline is modified. (Tentative).
+    // https://github.com/w3c/csswg-drafts/issues/5653
+    await assert_width(element, '100px');
+
+    element.style.animationPlayState = 'running';
+    await assert_width(element, '120px');
+  }, 'Switching timelines and pausing at the same time');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-frame-size-changed-ref.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-frame-size-changed-ref.html
new file mode 100644
index 0000000000..ea7628ac72
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-frame-size-changed-ref.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<title>Reference for the default scroll() timeline</title>
+<style>
+  html {
+    min-height: 100%;
+    padding-bottom: 50px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    transform: translateY(100px);
+  }
+
+  * {
+    margin-top: 0px;
+    margin-bottom: 0px;
+  }
+</style>
+
+<div id="box"></div>
+
+<script>
+  window.addEventListener('load', function() {
+    // Move the scroller to halfway.
+    const scroller = document.scrollingElement;
+    const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+    scroller.scrollTop = 0.5 * maxScroll;
+  });
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-frame-size-changed.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-frame-size-changed.html
new file mode 100644
index 0000000000..fb0eb8aa17
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-frame-size-changed.html
@@ -0,0 +1,67 @@
+<!DOCTYPE html>
+<html class="reftest-wait">
+<title>The default scroll() timeline when the frame size changed</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<meta name="assert" content="CSS animation correctly updates values when using
+                             the default scroll() timeline and update the
+                             frame size">
+<link rel="match" href="scroll-timeline-frame-size-changed-ref.html">
+
+<style>
+  @keyframes update {
+    from { transform: translateY(0px); }
+    to { transform: translateY(200px); }
+  }
+
+  html {
+    min-height: 100%;
+    padding-bottom: 100px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    animation: update 1s linear;
+    animation-timeline: scroll();
+  }
+
+  #covered {
+    width: 100px;
+    height: 100px;
+    background-color: red;
+  }
+
+  * {
+    margin-top: 0px;
+    margin-bottom: 0px;
+  }
+</style>
+
+<div id="box"></div>
+<div id="covered"></div>
+
+<script src="/web-animations/testcommon.js"></script>
+<script>
+  document.documentElement.addEventListener('TestRendered', async () => {
+    runTest();
+  }, { once: true });
+
+  async function runTest() {
+    const scroller = document.scrollingElement;
+
+    await waitForCompositorReady();
+
+    // Move the scroller to the 25% point.
+    const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+    scroller.scrollTop = 0.25 * maxScroll;
+    await waitForNextFrame();
+
+    // Update scroll range to make the current position become 50% point.
+    scroller.style.paddingBottom = "50px";
+    await waitForNextFrame();
+
+    document.documentElement.classList.remove("reftest-wait");
+  }
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-in-container-query.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-in-container-query.html
new file mode 100644
index 0000000000..d6a8ba8e60
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-in-container-query.html
@@ -0,0 +1,74 @@
+<!DOCTYPE html>
+<title>scroll-timeline and container queries</title>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#scroll-timeline-shorthand">
+<link rel="help" src="https://drafts.csswg.org/css-contain-3/#container-queries">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  #outer {
+    height: 100px;
+    width: 150px;
+  }
+
+  #container {
+    container-type: size;
+  }
+
+  #scroller {
+    overflow: auto;
+    width: auto;
+    height: 100px;
+  }
+  #scroller > div {
+    height: 200px;
+  }
+
+  /* This does not apply initially. */
+  @container (width > 200px) {
+    #scroller {
+      scroll-timeline: timeline;
+    }
+  }
+
+  @keyframes expand {
+    from { background-color: rgb(100, 100, 100); }
+    to { background-color: rgb(200, 200, 200); }
+  }
+  #element {
+    height: 10px;
+    width: 10px;
+    animation: expand 10s linear;
+    animation-timeline: timeline;
+    background-color: rgb(0, 0, 0);
+  }
+</style>
+<div id=outer>
+  <div id=container>
+    <div id=scroller>
+      <div></div>
+    </div>
+    <div id=element>
+    </div>
+  </div>
+</div>
+<script>
+  setup(assert_implements_animation_timeline);
+
+  promise_test(async (t) => {
+    element.offsetTop;
+    scroller.scrollTop = 50;
+    await waitForNextFrame();
+    // Unknown timeline, time held at zero.
+    assert_equals(getComputedStyle(element).backgroundColor, 'rgb(100, 100, 100)');
+    // This causes the timeline to be created.
+    outer.style.width = '250px';
+    // Check value with getComputedStyle immediately, which is the unanimated
+    // value since the scroll timeline is inactive before the next frame.
+    assert_equals(getComputedStyle(element).backgroundColor, 'rgb(0, 0, 0)');
+    // Also check value after one frame.
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element).backgroundColor, 'rgb(150, 150, 150)');
+  }, 'Timeline appearing via container queries');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-inactive.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-inactive.html
new file mode 100644
index 0000000000..92165d7046
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-inactive.html
@@ -0,0 +1,51 @@
+<!DOCTYPE html>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#scroll-timelines">
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#avoiding-cycles">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<style>
+  #scroller {
+    overflow: scroll;
+    width: 100px;
+    height: 100px;
+  }
+  #contents {
+    height: 200px;
+  }
+  @keyframes expand {
+    from { width: 100px; }
+    to { width: 200px; }
+  }
+  #element {
+    width: 0px;
+    animation: expand 10s linear paused;
+    animation-timeline: timeline;
+  }
+</style>
+<div id="container">
+  <div id=element></div>
+</div>
+<script>
+
+promise_test(async (t) => {
+  let div = document.createElement('div');
+  div.setAttribute('id', 'scroller');
+  div.style.scrollTimeline = 'timeline';
+  div.innerHTML = '<div id=contents></div>';
+  try {
+    container.insertBefore(div, element);
+
+    // The source has no layout box at the time the scroll timeline is created.
+    assert_equals(getComputedStyle(element).width, '0px');
+    scroller.offsetTop; // Ensure a layout box for the scroller.
+    // Wait for an update to the timeline state:
+    await waitForNextFrame();
+    // The timeline should now be active, and the animation should apply:
+    assert_equals(getComputedStyle(element).width, '100px');
+  } finally {
+    div.remove();
+  }
+}, 'Animation does not apply when timeline is initially inactive');
+
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-inline-orientation-ref.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-inline-orientation-ref.html
new file mode 100644
index 0000000000..7b87b1db39
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-inline-orientation-ref.html
@@ -0,0 +1,32 @@
+<!DOCTYPE html>
+<title>Reference for scroll timeline with inline orientation and root scroller</title>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<style>
+  html {
+    min-width: 100%;
+    padding-right: 100px;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    transform: translateX(100px);
+  }
+
+  * {
+    margin-left: 0px;
+    margin-right: 0px;
+  }
+</style>
+
+<div id="box"></div>
+
+<script>
+  window.addEventListener('load', function() {
+    // Move the scroller to halfway.
+    const scroller = document.scrollingElement;
+    const maxScroll = scroller.scrollWidth - scroller.clientWidth;
+    scroller.scrollLeft = 0.5 * maxScroll;
+  });
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-inline-orientation.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-inline-orientation.html
new file mode 100644
index 0000000000..52b7427f2d
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-inline-orientation.html
@@ -0,0 +1,68 @@
+<!DOCTYPE HTML>
+<html class="reftest-wait">
+<title>Scroll timeline with inline orientation and root scroller</title>
+<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1">
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#descdef-scroll-timeline-orientation">
+<link rel="help" href="https://drafts.csswg.org/css-animations-2/#animation-timeline">
+<meta name="assert" content="CSS animation correctly updates values when using the inline orientation">
+<link rel="match" href="scroll-timeline-inline-orientation-ref.html">
+
+<style>
+  @keyframes update {
+    from { transform: translateX(0px); }
+    to { transform: translateX(200px); }
+  }
+
+  html {
+    min-width: 100%;
+    padding-right: 100px;
+    font-size: 0;
+  }
+
+  #box {
+    width: 100px;
+    height: 100px;
+    background-color: green;
+    animation: update 1s linear;
+    animation-timeline: scroll(inline root);
+    display: inline-block;
+  }
+
+  #covered {
+    width: 100px;
+    height: 100px;
+    background-color: red;
+    display: inline-block;
+  }
+
+  * {
+    margin-left: 0px;
+    margin-right: 0px;
+  }
+</style>
+
+<div id="box"></div>
+<div id="covered"></div>
+
+<script src="/web-animations/testcommon.js"></script>
+<script>
+  document.documentElement.addEventListener('TestRendered', async () => {
+    runTest();
+  }, { once: true });
+
+  async function runTest() {
+    const scroller = document.scrollingElement;
+
+    await waitForCompositorReady();
+
+    // Move the scroller to the halfway point.
+    const maxScroll = scroller.scrollWidth - scroller.clientWidth;
+    scroller.scrollLeft = 0.5 * maxScroll;
+
+    await waitForNextFrame();
+    await waitForNextFrame();
+
+    document.documentElement.classList.remove("reftest-wait");
+  }
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-multi-pass.tentative.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-multi-pass.tentative.html
new file mode 100644
index 0000000000..91668ada5b
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-multi-pass.tentative.html
@@ -0,0 +1,109 @@
+<!DOCTYPE html>
+<title>ScrollTimelines may trigger multiple style/layout passes</title>
+<link rel="help" src="https://github.com/w3c/csswg-drafts/issues/5261">
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#avoiding-cycles">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes expand_width {
+    from { width: 100px; }
+    to { width: 100px; }
+  }
+  @keyframes expand_height {
+    from { height: 100px; }
+    to { height: 100px; }
+  }
+  main {
+    height: 0px;
+    overflow: hidden;
+  }
+  .scroller {
+    height: 100px;
+    overflow: scroll;
+  }
+  .scroller > div {
+    height: 200px;
+  }
+  #element1 {
+    width: 1px;
+    animation: expand_width 10s;
+    animation-timeline: timeline1;
+  }
+  #element2 {
+    height: 1px;
+    animation: expand_height 10s;
+    animation-timeline: timeline2;
+  }
+</style>
+<main id=main>
+  <div id=element1></div>
+  <div>
+    <div id=element2></div>
+  </div>
+</main>
+<script>
+    setup(assert_implements_animation_timeline);
+
+    function insertScroller(timeline_name) {
+      let scroller = document.createElement('div');
+      scroller.classList.add('scroller');
+      scroller.style.scrollTimeline = timeline_name;
+      scroller.append(document.createElement('div'));
+      main.insertBefore(scroller, element1);
+    }
+
+    promise_test(async () => {
+      await waitForNextFrame();
+
+      let events1 = [];
+      let events2 = [];
+
+      insertScroller('timeline1');
+      // Even though the scroller was just inserted into the DOM, |timeline1|
+      // remains inactive until the next frame.
+      //
+      // https://drafts.csswg.org/scroll-animations-1/#avoiding-cycles
+      assert_equals(getComputedStyle(element1).width, '1px');
+      (new ResizeObserver(entries => {
+        events1.push(entries);
+        insertScroller('timeline2');
+        assert_equals(getComputedStyle(element2).height, '1px');
+      })).observe(element1);
+
+      (new ResizeObserver(entries => {
+        events2.push(entries);
+      })).observe(element2);
+
+      await waitForNextFrame();
+
+      // According to the basic rules of the spec [1], the timeline is
+      // inactive at the time the resize observer event was delivered, because
+      // #scroller1 did not have a layout box at the time style recalc for
+      // #element1 happened.
+      //
+      // However, an additional style/layout pass should take place
+      // (before resize observer deliveries) if we detect new ScrollTimelines
+      // in this situation, hence we ultimately do expect the animation to
+      // apply [2].
+      //
+      // [1] https://drafts.csswg.org/scroll-animations-1/#avoiding-cycles
+      // [2] https://github.com/w3c/csswg-drafts/issues/5261
+      assert_equals(events1.length, 1);
+      assert_equals(events1[0].length, 1);
+      assert_equals(events1[0][0].contentBoxSize.length, 1);
+      assert_equals(events1[0][0].contentBoxSize[0].inlineSize, 100);
+
+      // ScrollTimelines created during the ResizeObserver should remain
+      // inactive during the frame they're created, so the ResizeObserver
+      // event should not reflect the animated value.
+      assert_equals(events2.length, 1);
+      assert_equals(events2[0].length, 1);
+      assert_equals(events2[0][0].contentBoxSize.length, 1);
+      assert_equals(events2[0][0].contentBoxSize[0].blockSize, 1);
+
+      assert_equals(getComputedStyle(element1).width, '100px');
+      assert_equals(getComputedStyle(element2).height, '100px');
+    }, 'Multiple style/layout passes occur when necessary');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-computed.tentative.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-computed.tentative.html
new file mode 100644
index 0000000000..1acb964ef7
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-computed.tentative.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/6674">
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/rewrite#scroll-timeline-name">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+</head>
+<style>
+  #outer { scroll-timeline-name: foo; }
+  #target { scroll-timeline-name: bar; }
+</style>
+<div id="outer">
+  <div id="target"></div>
+</div>
+<script>
+test_computed_value('scroll-timeline-name', 'initial', 'none');
+test_computed_value('scroll-timeline-name', 'inherit', 'foo');
+test_computed_value('scroll-timeline-name', 'unset', 'none');
+test_computed_value('scroll-timeline-name', 'revert', 'none');
+test_computed_value('scroll-timeline-name', 'none');
+test_computed_value('scroll-timeline-name', 'test');
+test_computed_value('scroll-timeline-name', 'tEst');
+
+test(() => {
+  let style = getComputedStyle(document.getElementById('target'));
+  assert_not_equals(Array.from(style).indexOf('scroll-timeline-name'), -1);
+}, 'The scroll-timeline-name property shows up in CSSStyleDeclaration enumeration');
+
+test(() => {
+  let style = document.getElementById('target').style;
+  assert_not_equals(style.cssText.indexOf('scroll-timeline-name'), -1);
+}, 'The scroll-timeline-name property shows up in CSSStyleDeclaration.cssText');
+
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-parsing.tentative.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-parsing.tentative.html
new file mode 100644
index 0000000000..a8f2e31650
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-parsing.tentative.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/6674">
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/rewrite#scroll-timeline-name">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+</head>
+<div id="target"></div>
+
+<script>
+
+test_valid_value('scroll-timeline-name', 'initial');
+test_valid_value('scroll-timeline-name', 'inherit');
+test_valid_value('scroll-timeline-name', 'unset');
+test_valid_value('scroll-timeline-name', 'revert');
+
+test_valid_value('scroll-timeline-name', 'none');
+test_valid_value('scroll-timeline-name', 'abc');
+test_valid_value('scroll-timeline-name', '  abc', 'abc');
+test_valid_value('scroll-timeline-name', 'aBc');
+test_valid_value('scroll-timeline-name', 'auto');
+
+test_invalid_value('scroll-timeline-name', 'default');
+test_invalid_value('scroll-timeline-name', '10px');
+test_invalid_value('scroll-timeline-name', 'foo bar');
+test_invalid_value('scroll-timeline-name', '"foo" "bar"');
+test_invalid_value('scroll-timeline-name', 'rgb(1, 2, 3)');
+test_invalid_value('scroll-timeline-name', '#fefefe');
+
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-tree-scoped.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-tree-scoped.html
new file mode 100644
index 0000000000..622a582cce
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-name-tree-scoped.html
@@ -0,0 +1,144 @@
+<!DOCTYPE html>
+<title>scroll-timelime-name and tree-scoped references</title>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#scroll-timelines-named">
+<link rel="help" src="https://drafts.csswg.org/css-scoping-1/#shadow-names">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="/resources/declarative-shadow-dom-polyfill.js"></script>
+
+<main id=main></main>
+<script>
+  function inflate(t, template) {
+    t.add_cleanup(() => main.replaceChildren());
+    main.append(template.content.cloneNode(true));
+    main.offsetTop;
+  }
+
+  setup(() => {
+    polyfill_declarative_shadow_dom(document);
+  });
+</script>
+<style>
+  @keyframes anim {
+    from { z-index: 100; }
+    to { z-index: 100; }
+  }
+</style>
+
+<template id=scroll_timeline_host>
+  <style>
+    .target {
+      animation: anim 10s linear;
+      animation-timeline: timeline;
+    }
+    main > .scroller {
+      scroll-timeline: timeline horizontal;
+    }
+  </style>
+  <div class=scroller>
+    <div class=scroller>
+      <template shadowroot=open>
+        <style>
+          :host {
+            scroll-timeline: timeline vertical;
+          }
+        </style>
+        <slot></slot>
+      </template>
+      <div class=target></div>
+    </div>
+  </div>
+  <style>
+  </style>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, scroll_timeline_host);
+    let target = main.querySelector('.target');
+    assert_equals(target.getAnimations().length, 1);
+    let anim = target.getAnimations()[0];
+    assert_not_equals(anim.timeline, null);
+    assert_equals(anim.timeline.axis, 'horizontal');
+  }, 'Outer animation can not see scroll timeline defined by :host');
+</script>
+
+
+<template id=scroll_timeline_slotted>
+  <style>
+    .target {
+      animation: anim 10s linear;
+      animation-timeline: timeline;
+    }
+    .host {
+      scroll-timeline: timeline horizontal;
+    }
+  </style>
+  <div class=host>
+    <template shadowroot=open>
+      <style>
+        ::slotted(.scroller) {
+          scroll-timeline: timeline vertical;
+        }
+      </style>
+      <slot></slot>
+    </template>
+    <div class=scroller>
+      <div class=target></div>
+    </div>
+  </div>
+  <style>
+  </style>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, scroll_timeline_slotted);
+    let target = main.querySelector('.target');
+    assert_equals(target.getAnimations().length, 1);
+    let anim = target.getAnimations()[0];
+    assert_not_equals(anim.timeline, null);
+    assert_equals(anim.timeline.axis, 'horizontal');
+  }, 'Outer animation can not see scroll timeline defined by ::slotted');
+</script>
+
+
+<template id=scroll_timeline_part>
+  <style>
+    .host {
+      scroll-timeline: timeline vertical;
+    }
+    .host::part(foo) {
+      scroll-timeline: timeline horizontal;
+    }
+  </style>
+  <div class=host>
+    <template shadowroot=open>
+      <style>
+          /* Not using 'anim' at document scope, due to https://crbug.com/1334534 */
+          @keyframes anim2 {
+            from { z-index: 100; background-color: green; }
+            to { z-index: 100; background-color: green; }
+          }
+        .target {
+          animation: anim2 10s linear;
+          animation-timeline: timeline;
+        }
+      </style>
+      <div part=foo>
+        <div class=target></div>
+      </div>
+    </template>
+  </div>
+  <style>
+  </style>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, scroll_timeline_part);
+    let target = main.querySelector('.host').shadowRoot.querySelector('.target');
+    assert_equals(target.getAnimations().length, 1);
+    let anim = target.getAnimations()[0];
+    assert_not_equals(anim.timeline, null);
+    assert_equals(anim.timeline.axis, 'horizontal');
+  }, 'Inner animation can see scroll timeline defined by ::part');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-nearest-dirty.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-nearest-dirty.html
new file mode 100644
index 0000000000..1a79c9bb22
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-nearest-dirty.html
@@ -0,0 +1,42 @@
+<!DOCTYPE html>
+<title>Unrelated style mutation does not affect anonymous timeline</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/scroll-animations/scroll-timelines/testcommon.js"></script>
+<script src="/css/css-animations/support/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { z-index: 100; }
+    to { z-index: 100; }
+  }
+  #scroller {
+    overflow: auto;
+    width: 100px;
+    height: 100px;
+  }
+  #element {
+    animation: anim forwards;
+    animation-timeline: scroll();
+  }
+  #spacer {
+    height: 200px;
+  }
+</style>
+<div id=scroller>
+  <div id=element></div>
+  <div id=spacer></div>
+</div>
+
+<script>
+setup(assert_implements_animation_timeline);
+
+promise_test(async () => {
+  await waitForCSSScrollTimelineStyle();
+  assert_equals(getComputedStyle(element).zIndex, '100');
+  // Unrelated style mutation does not change the effect value:
+  element.style.color = 'green';
+  assert_equals(getComputedStyle(element).zIndex, '100');
+});
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-paused-animations.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-paused-animations.html
new file mode 100644
index 0000000000..54518a5e87
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-paused-animations.html
@@ -0,0 +1,95 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Scroll timeline with paused animations</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://drafts.csswg.org/css-animations/#animation-play-state">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/scroll-animations/scroll-timelines/testcommon.js"></script>
+<script src="/css/css-animations/support/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { width: 100px; }
+    to { width: 200px; }
+  }
+
+  .fill-vh {
+    width: 100px;
+    height: 100vh;
+  }
+</style>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+setup(assert_implements_animation_timeline);
+
+async function resetScrollPosition() {
+  // Reset to 0 so we don't affect following tests.
+  document.scrollingElement.scrollTop = 0;
+  return waitForNextFrame();
+}
+
+promise_test(async t => {
+  const div = addDiv(t, { style: 'width: 50px; height: 100px;' });
+  const filling = addDiv(t, { class: 'fill-vh' });
+  const scroller = document.scrollingElement;
+  t.add_cleanup(resetScrollPosition);
+
+  div.style.animation = 'anim 100s linear paused';
+  div.style.animationTimeline = 'scroll(root)';
+  await waitForCSSScrollTimelineStyle();
+
+  const anim = div.getAnimations()[0];
+  await anim.ready;
+  assert_percents_equal(anim.currentTime, 0, 'timeline time reset');
+  assert_equals(getComputedStyle(div).width, '100px');
+
+  const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+  scroller.scrollTop = maxScroll;
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(div).width, '100px');
+
+}, 'Test that the scroll animation is paused');
+
+promise_test(async t => {
+  const div = addDiv(t, { style: 'width: 50px; height: 100px;' });
+  const filling = addDiv(t, { class: 'fill-vh' });
+  const scroller = document.scrollingElement;
+  await waitForNextFrame();
+
+  div.style.animation = 'anim 100s linear forwards';
+  div.style.animationTimeline = 'scroll(root)';
+  await waitForCSSScrollTimelineStyle();
+
+  const anim = div.getAnimations()[0];
+  await anim.ready;
+  assert_percents_equal(anim.currentTime, 0, 'timeline time reset');
+  assert_equals(getComputedStyle(div).width, '100px');
+
+  await waitForNextFrame();
+  const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+  scroller.scrollTop = maxScroll;
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(div).width, '200px');
+
+  div.style.animationPlayState = 'paused';
+  assert_equals(anim.playState, 'paused');
+  assert_equals(getComputedStyle(div).width, '200px',
+                'Current time preserved when pause-pending.');
+  assert_true(anim.pending,
+              'Pending state after changing animationPlayState');
+  await anim.ready;
+  assert_equals(getComputedStyle(div).width, '200px',
+                'Current time preserved when paused.');
+  assert_percents_equal(anim.timeline.currentTime, 100);
+  document.scrollingElement.scrollTop = 0;
+  await waitForNextFrame();
+  assert_percents_equal(anim.timeline.currentTime, 0);
+  assert_equals(getComputedStyle(div).width, '200px');
+}, 'Test that the scroll animation is paused by updating animation-play-state');
+
+</script>
+</body>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-responsiveness-from-endpoint.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-responsiveness-from-endpoint.html
new file mode 100644
index 0000000000..71d3699077
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-responsiveness-from-endpoint.html
@@ -0,0 +1,62 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Root-scrolling timeline with animation moving from end point</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<link rel="help" href="https://drafts.csswg.org/web-animations/#update-an-animations-finished-state">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/css-animations/support/testcommon.js"></script>
+<script src="/scroll-animations/scroll-timelines/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+
+<style>
+  @keyframes anim {
+    from { width: 100px; }
+    to { width: 200px; }
+  }
+
+  .fill-vh {
+    width: 100px;
+    height: 100vh;
+  }
+</style>
+<body>
+<div id="log"></div>
+<script>
+'use strict';
+
+setup(assert_implements_animation_timeline);
+
+promise_test(async t => {
+  const div = addDiv(t, { style: 'width: 50px; height: 100px;' });
+  const filling = addDiv(t, { class: 'fill-vh' });
+  const scroller = document.scrollingElement;
+  scroller.scrollTop = 0;
+  await waitForNextFrame();
+
+  div.style.animation = 'anim 100s linear';
+  div.style.animationTimeline = 'scroll(root)';
+  await waitForCSSScrollTimelineStyle();
+
+  const anim = div.getAnimations()[0];
+  await anim.ready;
+  assert_percents_equal(anim.timeline.currentTime, 0,
+                        'Timeline time when animation is ready');
+  assert_equals(getComputedStyle(div).width, '100px',
+                'Width at animation start');
+
+  await waitForNextFrame();
+  const maxScroll = scroller.scrollHeight - scroller.clientHeight;
+  scroller.scrollTop = maxScroll;
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(div).width, '200px',
+                'Width at scroll limit');
+
+  document.scrollingElement.scrollTop = 0;
+  await waitForNextFrame();
+  assert_equals(getComputedStyle(div).width, '100px',
+                'Width after reset to scroll top');
+}, 'Test that the scroll animation is still responsive after moving from 100%');
+
+</script>
+</body>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-root-dirty.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-root-dirty.html
new file mode 100644
index 0000000000..1c0b73ab45
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-root-dirty.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<title>Unrelated style mutation does not affect anonymous timeline (root)</title>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#scroll-notation">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/scroll-animations/scroll-timelines/testcommon.js"></script>
+<script src="/css/css-animations/support/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { z-index: 100; }
+    to { z-index: 100; }
+  }
+  #element {
+    animation: anim forwards;
+    animation-timeline: scroll(root);
+  }
+  #spacer {
+    height: 200vh;
+  }
+</style>
+<div id=element></div>
+<div id=spacer></div>
+
+<script>
+setup(assert_implements_animation_timeline);
+
+promise_test(async () => {
+  await waitForCSSScrollTimelineStyle();
+  assert_equals(getComputedStyle(element).zIndex, '100');
+  // Unrelated style mutation does not change the effect value:
+  element.style.color = 'green';
+  assert_equals(getComputedStyle(element).zIndex, '100');
+});
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-sampling.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-sampling.html
new file mode 100644
index 0000000000..1fe354edfd
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-sampling.html
@@ -0,0 +1,46 @@
+<!DOCTYPE html>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#avoiding-cycles">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<style>
+  #scroller {
+    overflow: hidden;
+    width: 100px;
+    height: 100px;
+    scroll-timeline: timeline;
+  }
+  #contents {
+    height: 200px;
+  }
+  @keyframes expand {
+    from { width: 100px; }
+    to { width: 200px; }
+  }
+  #element {
+    width: 0px;
+    animation: expand 10s linear;
+    animation-timeline: timeline;
+  }
+  /* Ensure stable expectations if feature is not supported */
+  @supports not (animation-timeline:foo) {
+    #element { animation-play-state: paused; }
+  }
+</style>
+<div id=scroller>
+  <div id=contents></div>
+</div>
+<div id=element></div>
+<script>
+  promise_test(async (t) => {
+    // The scroll timeline is initially inactive until the first frame.
+    assert_equals(getComputedStyle(element).width, '0px');
+    await waitForNextFrame();
+    scroller.scrollTop = 50;
+    // Scrolling position should not yet be reflected in the animation,
+    // since the new scroll position has not yet been sampled.
+    assert_equals(getComputedStyle(element).width, '100px');
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(element).width, '150px');
+  }, 'Scroll position is sampled once per frame');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-shorthand.tentative.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-shorthand.tentative.html
new file mode 100644
index 0000000000..b340ff34ff
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-shorthand.tentative.html
@@ -0,0 +1,41 @@
+<!DOCTYPE html>
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/6674">
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/rewrite#scroll-timeline-axis">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script src="/css/support/shorthand-testcommon.js"></script>
+<div id="target"></div>
+<script>
+test_valid_value('scroll-timeline', 'block none', 'block');
+test_valid_value('scroll-timeline', 'none inline', 'inline');
+test_valid_value('scroll-timeline', 'horizontal abc');
+test_valid_value('scroll-timeline', 'inline abc');
+test_valid_value('scroll-timeline', 'inline aBc');
+test_valid_value('scroll-timeline', 'vertical none', 'vertical');
+test_valid_value('scroll-timeline', 'inline inline');
+test_valid_value('scroll-timeline', 'abc');
+test_valid_value('scroll-timeline', 'inline');
+
+test_invalid_value('scroll-timeline', '');
+test_invalid_value('scroll-timeline', 'abc abc');
+
+test_computed_value('scroll-timeline', 'block none', 'block');
+test_computed_value('scroll-timeline', 'abc inline', 'inline abc');
+test_computed_value('scroll-timeline', 'none vertical', 'vertical');
+test_computed_value('scroll-timeline', 'horizontal abc');
+test_computed_value('scroll-timeline', 'vertical vertical');
+test_computed_value('scroll-timeline', 'abc');
+
+test_shorthand_value('scroll-timeline', 'vertical abc',
+{
+  'scroll-timeline-axis': 'vertical',
+  'scroll-timeline-name': 'abc',
+});
+test_shorthand_value('scroll-timeline', 'horizontal inline',
+{
+  'scroll-timeline-axis': 'horizontal',
+  'scroll-timeline-name': 'inline',
+});
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/scroll-timeline-sibling-gcs.html b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-sibling-gcs.html
new file mode 100644
index 0000000000..6062e795f4
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/scroll-timeline-sibling-gcs.html
@@ -0,0 +1,52 @@
+<!DOCTYPE html>
+<title>scroll-timeline and container queries</title>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#scroll-timeline-shorthand">
+<link rel="help" src="https://drafts.csswg.org/css-contain-3/#container-queries">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  #scroller {
+    overflow: auto;
+    width: auto;
+    height: 100px;
+  }
+  #scroller > div {
+    height: 200px;
+  }
+
+  @keyframes anim {
+    from { background-color: rgb(100, 100, 100); }
+    to { background-color: rgb(200, 200, 200); }
+  }
+  #element {
+    height: 10px;
+    width: 10px;
+    animation: anim 10s linear;
+    animation-timeline: timeline;
+    background-color: rgb(0, 0, 0);
+  }
+</style>
+<div>
+  <div id=scroller>
+    <div></div>
+  </div>
+  <div>
+    <div id=element></div>
+  </div>
+</div>
+<script>
+  setup(assert_implements_animation_timeline);
+
+  promise_test(async (t) => {
+    element.offsetTop;
+    scroller.scrollTop = 50;
+    await waitForNextFrame();
+    // Unknown timeline, time held at zero.
+    assert_equals(getComputedStyle(element).backgroundColor, 'rgb(100, 100, 100)');
+    scroller.style.scrollTimeline = 'timeline';
+    await waitForCSSScrollTimelineStyle();
+    assert_equals(getComputedStyle(element).backgroundColor, 'rgb(150, 150, 150)');
+  }, 'Timelines appearing on preceding siblings are visible to getComputedStyle');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/support/testcommon.js b/testing/web-platform/tests/scroll-animations/css/support/testcommon.js
new file mode 100644
index 0000000000..66bc27bb10
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/support/testcommon.js
@@ -0,0 +1,19 @@
+'use strict';
+
+/**
+ * Returns a Promise that is resolved after a CSS scroll timeline is created (as
+ * the result of a style change) and a snapshot has been taken, so that the
+ * animation style is correctly reflected by getComputedStyle().
+ * Technically, this only takes a full frame update. We implement this as two
+ * requestAnimationFrame callbacks because the result will be available at the
+ * beginning of the second frame.
+ */
+async function waitForCSSScrollTimelineStyle() {
+  await waitForNextFrame();
+  await waitForNextFrame();
+}
+
+function assert_implements_animation_timeline() {
+  assert_implements(CSS.supports('animation-timeline:foo'),
+      'animation-timeline not supported');
+}
diff --git a/testing/web-platform/tests/scroll-animations/css/timeline-range-name-offset-in-keyframes.tentative.html b/testing/web-platform/tests/scroll-animations/css/timeline-range-name-offset-in-keyframes.tentative.html
new file mode 100644
index 0000000000..993046c5f2
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/timeline-range-name-offset-in-keyframes.tentative.html
@@ -0,0 +1,94 @@
+<!DOCTYPE html>
+<html>
+<meta charset="utf-8">
+<title>Timeline offset in Animation Keyframes</title>
+<link rel="help" href="https://w3c.github.io/csswg-drafts/scroll-animations-1/#named-range-keyframes">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes fade-in-out-animation {
+    enter 0%, exit 100% { opacity: 0 }
+    enter 100%, exit 0% { opacity: 1 }
+  }
+
+  #subject {
+    background-color:  rgba(0, 0, 255);
+    height: 200px;
+    width: 200px;
+    view-timeline-name: foo;
+    animation: linear 1s both fade-in-out-animation;
+    animation-timeline: foo;
+  }
+
+  #container {
+    border:  5px solid black;
+    height:  400px;
+    width:  400px;
+    overflow-y:  scroll;
+    resize: both;
+  }
+
+  .spacer {
+    height: 600px;
+    width: 100%;
+  }
+</style>
+<body onload="runTests()">
+  <div id="container">
+    <div class="spacer"></div>
+    <div id="subject"></div>
+    <div class="spacer"></div>
+  </div>
+</body>
+
+<script type="text/javascript">
+  setup(assert_implements_animation_timeline);
+
+  function runTests() {
+    promise_test(async t => {
+      // scrollTop=200 to 400 is the enter range
+      container.scrollTop = 200;
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(subject).opacity, '0', 'Effect at enter 0%');
+
+      container.scrollTop = 300;
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(subject).opacity, '0.5', 'Effect at enter 50%');
+
+      container.scrollTop = 400;
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(subject).opacity, '1', 'Effect at enter 100%');
+
+      // scrollTop=600-800 is the exit range
+      container.scrollTop = 600;
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(subject).opacity, '1', 'Effect at exit 0%');
+
+      container.scrollTop = 700;
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(subject).opacity, '0.5', 'Effect at exit 50%');
+
+      container.scrollTop = 800;
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(subject).opacity, '0', 'Effect at exit 100%');
+
+      // First change scrollTop so that you are at enter 100%, then resize the container in a way
+      // that scrollTop is the same, but now the animation is at enter 50% and check opacity.
+      // After changing the height of container, scrollTop=300-500 is the enter range
+      container.scrollTop = 400;
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(subject).opacity, '1', 'Effect at enter 100%');
+      container.style.height = '300px';
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(subject).opacity, '0.5', 'Effect at enter 50%');
+
+      // After changing the height of container, scrollTop=600-800 is still the exit range
+      container.scrollTop = 700;
+      await waitForNextFrame();
+      assert_equals(getComputedStyle(subject).opacity, '0.5', 'Effect at exit 50%');
+    });
+  }
+</script>
+</html>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-animation.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-animation.html
new file mode 100644
index 0000000000..b816bb6897
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-animation.html
@@ -0,0 +1,219 @@
+<!DOCTYPE html>
+<title>Animations using view-timeline</title>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#view-timelines-named">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { z-index: 0; }
+    to { z-index: 100; }
+  }
+  .vertical-scroller {
+    overflow: auto;
+    width: 100px;
+    height: 100px;
+  }
+  .vertical-scroller > div {
+    height: 50px;
+    z-index: -1;
+  }
+  .horizontal-scroller {
+    overflow: auto;
+    width: 100px;
+    height: 100px;
+    writing-mode: vertical-lr;
+  }
+  .horizontal-scroller > div {
+    width: 50px;
+    z-index: -1;
+  }
+</style>
+<main id=main></main>
+<script>
+  setup(assert_implements_animation_timeline);
+
+  function inflate(t, template) {
+    t.add_cleanup(() => main.replaceChildren());
+    main.append(template.content.cloneNode(true));
+  }
+  async function scrollTop(e, value) {
+    e.scrollTop = value;
+    await waitForNextFrame();
+  }
+  async function scrollLeft(e, value) {
+    e.scrollLeft = value;
+    await waitForNextFrame();
+  }
+</script>
+
+<template id=default_view_timeline>
+  <style>
+    #target {
+      view-timeline: t1;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=vertical-scroller>
+    <div></div>           <!-- [0px,   50px]  -->
+    <div></div>           <!-- [50px,  100px] -->
+    <div></div>           <!-- [100px, 150px] -->
+    <div id=target></div> <!-- [150px, 200px] -->
+    <div></div>           <!-- [200px, 250px] -->
+    <div></div>           <!-- [250px, 300px] -->
+    <div></div>           <!-- [300px, 350px] -->
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, default_view_timeline);
+    assert_equals(getComputedStyle(target).zIndex, '-1');
+    await scrollTop(scroller, 25);
+    assert_equals(getComputedStyle(target).zIndex, '-1');
+    await scrollTop(scroller, 50); // 0% (enter 0%)
+    assert_equals(getComputedStyle(target).zIndex, '0');
+    await scrollTop(scroller, 125); // 50%
+    assert_equals(getComputedStyle(target).zIndex, '50');
+    await scrollTop(scroller, 200); // 100% (exit 100%)
+    assert_equals(getComputedStyle(target).zIndex, '100');
+    await scrollTop(scroller, 225);
+    assert_equals(getComputedStyle(target).zIndex, '-1');
+  }, 'Default view-timeline');
+</script>
+
+<template id=horizontal_timeline>
+  <style>
+    #target {
+      view-timeline: t1 horizontal;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=horizontal-scroller>
+    <div></div>           <!-- [0px,   50px]  -->
+    <div></div>           <!-- [50px,  100px] -->
+    <div></div>           <!-- [100px, 150px] -->
+    <div id=target></div> <!-- [150px, 200px] -->
+    <div></div>           <!-- [200px, 250px] -->
+    <div></div>           <!-- [250px, 300px] -->
+    <div></div>           <!-- [300px, 350px] -->
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, horizontal_timeline);
+    assert_equals(getComputedStyle(target).zIndex, '-1');
+    await scrollLeft(scroller, 25);
+    assert_equals(getComputedStyle(target).zIndex, '-1');
+    await scrollLeft(scroller, 50); // 0% (enter 0%)
+    assert_equals(getComputedStyle(target).zIndex, '0');
+    await scrollLeft(scroller, 125); // 50%
+    assert_equals(getComputedStyle(target).zIndex, '50');
+    await scrollLeft(scroller, 200); // 100% (exit 100%)
+    assert_equals(getComputedStyle(target).zIndex, '100');
+    await scrollLeft(scroller, 225);
+    assert_equals(getComputedStyle(target).zIndex, '-1');
+  }, 'Horizontal view-timeline');
+</script>
+
+<template id=multiple_timelines>
+  <style>
+    #timelines {
+      view-timeline: tv vertical, th horizontal;
+      background-color: red;
+    }
+    #scroller {
+      width: 100px;
+      height: 100px;
+      overflow: hidden;
+      display: grid;
+      grid-template-columns: 50px 50px 50px 50px 50px 50px 50px;
+      grid-template-row: 50px 50px 50px 50px 50px 50px 50px;
+    }
+    #scroller > div {
+      z-index: -1;
+      width: 50px;
+      height: 50px;
+    }
+    #target_v {
+      animation: anim 1s linear;
+      animation-timeline: tv;
+    }
+    #target_h {
+      animation: anim 1s linear;
+      animation-timeline: th;
+    }
+  </style>
+  <div id=scroller>
+    <!-- Created dynamically -->
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, multiple_timelines);
+
+    // Create a 350px x 350px grid (7x7 items of 50x50px each), with the
+    // timelines at item [3,3], an element attached to the horizontal timeline
+    // at [4,3], and an element attached to the vertical timeline at [3,4].
+
+    // x  x  x  x  x  x  x
+    // x  x  x  x  x  x  x
+    // x  x  x  x  x  x  x
+    // x  x  x  T  H  x  x
+    // x  x  x  V  x  x  x
+    // x  x  x  x  x  x  x
+    // x  x  x  x  x  x  x
+    // x  x  x  x  x  x  x
+
+    let grid_size = 7;
+    for (let i = 0; i < (grid_size*grid_size); ++i) {
+      let div = document.createElement('div');
+      if (i == (3 * grid_size + 3))
+        div.id = 'timelines';
+      if (i == (3 * grid_size + 4))
+        div.id = 'target_h';
+      if (i == (4 * grid_size + 3))
+        div.id = 'target_v';
+      scroller.append(div);
+    }
+
+    assert_equals(getComputedStyle(target_v).zIndex, '-1');
+    assert_equals(getComputedStyle(target_h).zIndex, '-1');
+
+    // First scroll vertically.
+    await scrollTop(scroller, 25);
+    assert_equals(getComputedStyle(target_v).zIndex, '-1');
+    assert_equals(getComputedStyle(target_h).zIndex, '-1');
+    await scrollTop(scroller, 50); // 0% (enter 0%)
+    assert_equals(getComputedStyle(target_v).zIndex, '0');
+    assert_equals(getComputedStyle(target_h).zIndex, '-1');
+    await scrollTop(scroller, 125); // 50%
+    assert_equals(getComputedStyle(target_v).zIndex, '50');
+    assert_equals(getComputedStyle(target_h).zIndex, '-1');
+    await scrollTop(scroller, 200); // 100% (exit 100%)
+    assert_equals(getComputedStyle(target_v).zIndex, '100');
+    assert_equals(getComputedStyle(target_h).zIndex, '-1');
+    await scrollTop(scroller, 225);
+    assert_equals(getComputedStyle(target_v).zIndex, '-1');
+    assert_equals(getComputedStyle(target_h).zIndex, '-1');
+
+    // Then horizontally.
+    await scrollLeft(scroller, 25);
+    assert_equals(getComputedStyle(target_v).zIndex, '-1');
+    assert_equals(getComputedStyle(target_h).zIndex, '-1');
+    await scrollLeft(scroller, 50); // 0% (enter 0%)
+    assert_equals(getComputedStyle(target_v).zIndex, '-1');
+    assert_equals(getComputedStyle(target_h).zIndex, '0');
+    await scrollLeft(scroller, 125); // 50%
+    assert_equals(getComputedStyle(target_v).zIndex, '-1');
+    assert_equals(getComputedStyle(target_h).zIndex, '50');
+    await scrollLeft(scroller, 200); // 100% (exit 100%)
+    assert_equals(getComputedStyle(target_v).zIndex, '-1');
+    assert_equals(getComputedStyle(target_h).zIndex, '100');
+    await scrollLeft(scroller, 225);
+    assert_equals(getComputedStyle(target_v).zIndex, '-1');
+    assert_equals(getComputedStyle(target_h).zIndex, '-1');
+  }, 'Multiple view-timelines on the same element');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-axis-computed.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-axis-computed.html
new file mode 100644
index 0000000000..f4649dab04
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-axis-computed.html
@@ -0,0 +1,37 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#view-timeline-axis">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+</head>
+<style>
+  #outer { view-timeline-axis: block, inline; }
+  #target { view-timeline-axis: vertical; }
+</style>
+<div id=outer>
+  <div id=target></div>
+</div>
+<script>
+test_computed_value('view-timeline-axis', 'initial', 'block');
+test_computed_value('view-timeline-axis', 'inherit', 'block, inline');
+test_computed_value('view-timeline-axis', 'unset', 'block');
+test_computed_value('view-timeline-axis', 'revert', 'block');
+test_computed_value('view-timeline-axis', 'block');
+test_computed_value('view-timeline-axis', 'inline');
+test_computed_value('view-timeline-axis', 'vertical');
+test_computed_value('view-timeline-axis', 'horizontal');
+test_computed_value('view-timeline-axis', 'block, inline');
+test_computed_value('view-timeline-axis', 'inline, block');
+test_computed_value('view-timeline-axis', 'block, vertical, horizontal, inline');
+test_computed_value('view-timeline-axis', 'inline, inline, inline, inline');
+
+test(() => {
+  let style = getComputedStyle(document.getElementById('target'));
+  assert_not_equals(Array.from(style).indexOf('view-timeline-axis'), -1);
+}, 'The view-timeline-axis property shows up in CSSStyleDeclaration enumeration');
+
+test(() => {
+  let style = document.getElementById('target').style;
+  assert_not_equals(style.cssText.indexOf('view-timeline-axis'), -1);
+}, 'The view-timeline-axis property shows up in CSSStyleDeclaration.cssText');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-axis-parsing.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-axis-parsing.html
new file mode 100644
index 0000000000..ffcc36c320
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-axis-parsing.html
@@ -0,0 +1,29 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#view-timeline-axis">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+</head>
+<div id="target"></div>
+<script>
+test_valid_value('view-timeline-axis', 'initial');
+test_valid_value('view-timeline-axis', 'inherit');
+test_valid_value('view-timeline-axis', 'unset');
+test_valid_value('view-timeline-axis', 'revert');
+
+test_valid_value('view-timeline-axis', 'block');
+test_valid_value('view-timeline-axis', 'inline');
+test_valid_value('view-timeline-axis', 'vertical');
+test_valid_value('view-timeline-axis', 'horizontal');
+test_valid_value('view-timeline-axis', 'block, inline');
+test_valid_value('view-timeline-axis', 'inline, block');
+test_valid_value('view-timeline-axis', 'block, vertical, horizontal, inline');
+test_valid_value('view-timeline-axis', 'inline, inline, inline, inline');
+
+test_invalid_value('view-timeline-axis', 'abc');
+test_invalid_value('view-timeline-axis', '10px');
+test_invalid_value('view-timeline-axis', 'auto');
+test_invalid_value('view-timeline-axis', 'none');
+test_invalid_value('view-timeline-axis', 'block inline');
+test_invalid_value('view-timeline-axis', 'block / inline');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-delay-animation.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-delay-animation.html
new file mode 100644
index 0000000000..dfb0e59f5d
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-delay-animation.html
@@ -0,0 +1,144 @@
+<!DOCTYPE html>
+<title>Animations using named timeline ranges</title>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#named-timeline-range">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { z-index: 0; background-color: skyblue;}
+    to { z-index: 100; background-color: coral; }
+  }
+  #scroller {
+    border:  10px solid lightgray;
+    overflow-y: scroll;
+    width: 200px;
+    height: 200px;
+  }
+  #target {
+    margin: 800px 0px;
+    width: 100px;
+    height: 100px;
+    z-index: -1;
+    background-color: green;
+  }
+</style>
+<main id=main>
+</main>
+<template>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  setup(assert_implements_animation_timeline);
+
+  function inflate(t, template) {
+    t.add_cleanup(() => main.replaceChildren());
+    main.append(template.content.cloneNode(true));
+  }
+  async function scrollTop(e, value) {
+    e.scrollTop = value;
+    await waitForNextFrame();
+  }
+  async function waitForAnimationReady(target) {
+    await waitForNextFrame();
+    await Promise.all(target.getAnimations().map(x => x.promise));
+  }
+  async function assertValueAt(scroller, target, args) {
+    await waitForAnimationReady(target);
+    await scrollTop(scroller, args.scrollTop);
+    assert_equals(getComputedStyle(target).zIndex, args.expected.toString());
+  }
+  function test_animation_delay(options) {
+    promise_test(async (t) => {
+      inflate(t, document.querySelector('template'));
+      let scroller = main.querySelector('#scroller');
+      let target = main.querySelector('#target');
+
+      target.style.viewTimeline = 't1 block';
+      // TODO(crbug.com/1375998): Create the timeline in a separate frame to
+      // work around a bug.
+      await waitForNextFrame();
+
+      target.style.animation = 'anim 10s linear';
+      target.style.animationTimeline = 't1';
+      target.style.animationDelayStart = options.startDelay;
+      target.style.animationDelayEnd = options.endDelay;
+
+      // Accommodates floating point precision errors at the endpoints.
+      target.style.animationFillMode = 'both';
+
+      // 0%
+      await assertValueAt(scroller, target,
+          { scrollTop: options.rangeStart, expected: 0 });
+      // 50%
+      await assertValueAt(scroller, target,
+          { scrollTop: (options.rangeStart + options.rangeEnd) / 2, expected: 50 });
+      // 100%
+      await assertValueAt(scroller, target,
+          { scrollTop: options.rangeEnd, expected: 100 });
+
+      // Test before/after phases (need to clear the fill mode for that).
+      target.style.animationFillMode = 'initial';
+      await assertValueAt(scroller, target,
+          { scrollTop: options.rangeStart - 10, expected: -1 });
+      await assertValueAt(scroller, target,
+          { scrollTop: options.rangeEnd + 10, expected: -1 });
+      // Check 50% again without fill mode.
+      await assertValueAt(scroller, target,
+          { scrollTop: (options.rangeStart + options.rangeEnd) / 2, expected: 50 });
+
+    }, `Animation with delays [${options.startDelay}, ${options.endDelay}]`);
+  }
+
+  test_animation_delay({
+    startDelay: 'initial',
+    endDelay: 'initial',
+    rangeStart: 600,
+    rangeEnd: 900
+  });
+
+  test_animation_delay({
+    startDelay: 'cover 0%',
+    endDelay: 'cover 100%',
+    rangeStart: 600,
+    rangeEnd: 900
+  });
+
+  test_animation_delay({
+    startDelay: 'contain 0%',
+    endDelay: 'contain 100%',
+    rangeStart: 700,
+    rangeEnd: 800
+  });
+
+  test_animation_delay({
+    startDelay: 'enter 0%',
+    endDelay: 'enter 100%',
+    rangeStart: 600,
+    rangeEnd: 700
+  });
+
+  test_animation_delay({
+    startDelay: 'exit 0%',
+    endDelay: 'exit 100%',
+    rangeStart: 800,
+    rangeEnd: 900
+  });
+
+  test_animation_delay({
+    startDelay: 'contain -50%',
+    endDelay: 'enter 200%',
+    rangeStart: 650,
+    rangeEnd: 800
+  });
+
+  test_animation_delay({
+    startDelay: 'enter 0%',
+    endDelay: 'exit 100%',
+    rangeStart: 600,
+    rangeEnd: 900
+  });
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-dynamic.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-dynamic.html
new file mode 100644
index 0000000000..74da8850d4
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-dynamic.html
@@ -0,0 +1,183 @@
+<!DOCTYPE html>
+<title>Changes to view-timeline are reflected in dependent elements</title>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#view-timeline-shorthand">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { z-index: 0; }
+    to { z-index: 100; }
+  }
+  .scroller {
+    overflow: hidden;
+    width: 100px;
+    height: 100px;
+  }
+  .scroller > div {
+    height: 100px;
+  }
+  #target {
+    height: 0px;
+    z-index: -1;
+  }
+</style>
+<main id=main></main>
+<script>
+  setup(assert_implements_animation_timeline);
+
+  function inflate(t, template) {
+    t.add_cleanup(() => main.replaceChildren());
+    main.append(template.content.cloneNode(true));
+    main.offsetTop;
+  }
+  async function scrollTop(e, value) {
+    e.scrollTop = value;
+    await waitForNextFrame();
+  }
+  async function scrollLeft(e, value) {
+    e.scrollLeft = value;
+    await waitForNextFrame();
+  }
+</script>
+
+<template id=dynamic_view_timeline_name>
+  <style>
+    .timeline {
+      view-timeline-name: t1;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div id=div75></div>
+    <div id=div25></div>
+    <div id=div_before></div>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, dynamic_view_timeline_name);
+
+    await scrollTop(scroller, 50);
+
+    // scrollTop=50 is 75% for div75.
+    div75.classList.add('timeline');
+    await waitForCSSScrollTimelineStyle();
+    assert_equals(getComputedStyle(target).zIndex, '75');
+
+    // scrollTop=50 is 25% for div25.
+    div25.classList.add('timeline');
+    await waitForCSSScrollTimelineStyle();
+    assert_equals(getComputedStyle(target).zIndex, '25');
+
+    // scrollTop=50 is before the timeline start for div_before.
+    div_before.classList.add('timeline');
+    await waitForCSSScrollTimelineStyle();
+    assert_equals(getComputedStyle(target).zIndex, '-1');
+    // Scroll to 25% (for div_before) to verify that we're linked to that
+    // timeline.
+    await scrollTop(scroller, 150);
+    assert_equals(getComputedStyle(target).zIndex, '25');
+
+    // Now we should be back to div25's timeline, although with the new
+    // scrollTop=150, it's actually at 75%.
+    div_before.classList.remove('timeline');
+    await waitForCSSScrollTimelineStyle();
+    assert_equals(getComputedStyle(target).zIndex, '75');
+  }, 'Dynamically changing view-timeline-name');
+</script>
+
+<template id=dynamic_view_timeline_axis>
+  <style>
+    #timeline {
+      width: 100px;
+      height: 100px;
+      margin: 100px;
+      view-timeline-name: t1;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div id=timeline style="background: red;"></div>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, dynamic_view_timeline_axis);
+
+    await scrollTop(scroller, 50); // 25% (vertical)
+    await scrollLeft(scroller, 20); // 10% (horizontal)
+
+    assert_equals(getComputedStyle(target).zIndex, '25');
+    timeline.style.viewTimelineAxis = 'horizontal';
+    await waitForCSSScrollTimelineStyle();
+    assert_equals(getComputedStyle(target).zIndex, '10');
+  }, 'Dynamically changing view-timeline-axis');
+</script>
+
+<template id=dynamic_view_timeline_inset>
+  <style>
+    #timeline {
+      width: 100px;
+      height: 100px;
+      margin: 100px;
+      view-timeline-name: t1;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div id=timeline style="background: red;"></div>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, dynamic_view_timeline_inset);
+
+    await scrollTop(scroller, 50); // 25% (without inset).
+
+    assert_equals(getComputedStyle(target).zIndex, '25');
+    timeline.style.viewTimelineInset = '0px 50px';
+    await waitForCSSScrollTimelineStyle();
+    assert_equals(getComputedStyle(target).zIndex, '0');
+  }, 'Dynamically changing view-timeline-inset');
+</script>
+
+<template id=timeline_display_none>
+  <style>
+    #timeline {
+      view-timeline-name: t1;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div></div>
+    <div id=timeline></div>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, timeline_display_none);
+
+    await scrollTop(scroller, 50);
+    assert_equals(getComputedStyle(target).zIndex, '25');
+    timeline.style.display = 'none';
+    assert_equals(getComputedStyle(target).zIndex, '-1');
+  }, 'Element with view-timeline becoming display:none');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-inset-animation.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-inset-animation.html
new file mode 100644
index 0000000000..a95086b62b
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-inset-animation.html
@@ -0,0 +1,768 @@
+<!DOCTYPE html>
+<title>Animations using view-timeline-inset</title>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#propdef-view-timeline-inset">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { z-index: 0; }
+    to { z-index: 100; }
+  }
+  #scroller {
+    overflow: hidden;
+    width: 80px;
+    height: 100px;
+  }
+  #target {
+    margin: 150px;
+    width: 50px;
+    height: 50px;
+    z-index: -1;
+  }
+</style>
+<main id=main></main>
+<script>
+  setup(assert_implements_animation_timeline);
+
+  function inflate(t, template) {
+    t.add_cleanup(() => main.replaceChildren());
+    main.append(template.content.cloneNode(true));
+  }
+  async function scrollTop(e, value) {
+    e.scrollTop = value;
+    await waitForNextFrame();
+  }
+  async function scrollLeft(e, value) {
+    e.scrollLeft = value;
+    await waitForNextFrame();
+  }
+  async function assertValueAt(scroller, target, args) {
+    if (args.scrollTop !== undefined)
+      await scrollTop(scroller, args.scrollTop);
+    if (args.scrollLeft !== undefined)
+      await scrollLeft(scroller, args.scrollLeft);
+    assert_equals(getComputedStyle(target).zIndex, args.expected.toString());
+  }
+</script>
+
+<!--
+  Explanation of scroll positions
+  ===============================
+
+  Please note the following:
+
+   - The scroller has a width x height of 80x100px.
+   - The content is 50x50px with a 150px margin on all sides.
+     In other words, the size of the scroller content is 200x200px.
+
+  This means that, for vertical direction scrolling, assuming no insets:
+
+   - The start offset is 50px (scroller height + 50px is 150px, which consumes
+     exactly the margin of the content).
+   - The end offset is 200px (this is where the bottom edge of the scroller has
+     just cleared the content).
+   - The halfway point is (50px + 200px) / 2 = 125px.
+
+  For horizontal direction scrolling, assuming no insets:
+
+   - The start offset is 70px (scroller width + 70px is 150px, which consumes
+     exactly the margin of the content).
+   - The end offset is 200px (this is where the left edge of the scroller has
+     just cleared the content).
+   - The halfway point is (70px + 200px) / 2 = 135px.
+
+  The start and end insets will adjust the start and end offsets accordingly,
+  and the expectations in this file explicitly write out those adjustments.
+  For example, if the start offset is normally 50px, but there's an inset of
+  10px, we'll expect 50px + 10px rather than 60px.
+
+  Halfway-point expectations write out the adjustment from the "normal"
+  halfway-point, e.g. for start-inset:10px and end-inset:20px, we expect
+  "125px + 5px" since (20-10)/2 == 5.
+
+  Finally, note that for right-to-left and bottom-to-top scrolling directions
+  scroll offsets go the in the negative direction. This is why some expectations
+  negate all the offsets.
+-->
+
+<template id=test_one_value>
+  <style>
+    #target {
+      view-timeline: t1;
+      view-timeline-inset: 10px;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=vertical>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_one_value);
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 10, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 0, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset with one value');
+</script>
+
+<template id=test_two_values>
+  <style>
+    #target {
+      view-timeline: t1;
+      view-timeline-inset: 10px 20px;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=vertical>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_two_values);
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset with two values');
+</script>
+
+<template id=test_em_values>
+  <style>
+    #target {
+      font-size: 10px;
+      view-timeline: t1;
+      view-timeline-inset: 10px 2em;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=vertical>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_em_values);
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset with em values');
+</script>
+
+<template id=test_percentage_values>
+  <style>
+    #target {
+      font-size: 10px;
+      view-timeline: t1;
+      view-timeline-inset: calc(5px + max(1%, 5%)) 20%;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=vertical>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_percentage_values);
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset with percentage values');
+</script>
+
+<template id=test_outset>
+  <style>
+    #target {
+      view-timeline: t1;
+      view-timeline-inset: -10px -20px;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=vertical>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_outset);
+    await assertValueAt(scroller, target, { scrollTop:20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 - 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 - 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 + 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:220, expected:-1 });
+  }, 'view-timeline-inset with negative values');
+</script>
+
+<template id=test_horizontal>
+  <style>
+    #target {
+      view-timeline: t1 horizontal;
+      view-timeline-inset: 10px 20px;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_horizontal);
+    await assertValueAt(scroller, target, { scrollLeft:20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollLeft:70 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollLeft:135 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollLeft:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollLeft:200, expected:-1 });
+  }, 'view-timeline-inset with horizontal scroller');
+</script>
+
+<template id=test_block>
+  <style>
+    #target {
+      view-timeline: t1 block;
+      view-timeline-inset: 10px 20px;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_block);
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset with block scroller');
+</script>
+
+<template id=test_inline>
+  <style>
+    #target {
+      view-timeline: t1 inline;
+      view-timeline-inset: 10px 20px;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_inline);
+    await assertValueAt(scroller, target, { scrollLeft:20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollLeft:70 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollLeft:135 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollLeft:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollLeft:200, expected:-1 });
+  }, 'view-timeline-inset with inline scroller');
+</script>
+
+<template id=test_auto_block>
+  <style>
+    #scroller {
+      scroll-padding-block: 10px 20px;
+    }
+    #target {
+      view-timeline: t1 block;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_block);
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset:auto, block');
+</script>
+
+<template id=test_auto_block_vertical_lr>
+  <style>
+    #scroller {
+      scroll-padding-block: 10px 20px;
+      writing-mode: vertical-lr;
+    }
+    #target {
+      view-timeline: t1 block;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_block_vertical_lr);
+    await assertValueAt(scroller, target, { scrollLeft:20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollLeft:70 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollLeft:135 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollLeft:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollLeft:200, expected:-1 });
+  }, 'view-timeline-inset:auto, block, vertical-lr');
+</script>
+
+<template id=test_auto_block_vertical_rl>
+  <style>
+    #scroller {
+      scroll-padding-block: 10px 20px;
+      writing-mode: vertical-rl;
+    }
+    #target {
+      view-timeline: t1 block;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_block_vertical_rl);
+    // Note: this represents horizontal scrolling from right to left.
+    await assertValueAt(scroller, target, { scrollLeft:-20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollLeft:-(70 + 20), expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollLeft:-(135 + 5), expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollLeft:-(200 - 10), expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollLeft:-200, expected:-1 });
+  }, 'view-timeline-inset:auto, block, vertical-rl');
+</script>
+
+<template id=test_auto_inline>
+  <style>
+    #scroller {
+      scroll-padding-inline: 10px 20px;
+    }
+    #target {
+      view-timeline: t1 inline;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_inline);
+    await assertValueAt(scroller, target, { scrollLeft:20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollLeft:70 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollLeft:135 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollLeft:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollLeft:200, expected:-1 });
+  }, 'view-timeline-inset:auto, inline');
+</script>
+
+<template id=test_auto_inline_vertical_rl>
+  <style>
+    #scroller {
+      scroll-padding-inline: 10px 20px;
+      writing-mode: vertical-rl;
+    }
+    #target {
+      view-timeline: t1 inline;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_inline_vertical_rl);
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset:auto, inline, vertical-rl');
+</script>
+
+<template id=test_auto_inline_vertical_lr>
+  <style>
+    #scroller {
+      scroll-padding-inline: 10px 20px;
+      writing-mode: vertical-lr;
+    }
+    #target {
+      view-timeline: t1 inline;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_inline_vertical_lr);
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset:auto, inline, vertical-lr');
+</script>
+
+<template id=test_auto_inline_rtl>
+  <style>
+    #scroller {
+      scroll-padding-inline: 10px 20px;
+      direction: rtl;
+    }
+    #target {
+      view-timeline: t1 inline;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_inline_rtl);
+    await assertValueAt(scroller, target, { scrollLeft:-20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollLeft:-(70 + 20), expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollLeft:-(135 + 5), expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollLeft:-(200 - 10), expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollLeft:-200, expected:-1 });
+  }, 'view-timeline-inset:auto, inline, rtl');
+</script>
+
+<template id=test_auto_inline_vertical_rl_rtl>
+  <style>
+    #scroller {
+      scroll-padding-inline: 10px 20px;
+      writing-mode: vertical-rl;
+      direction: rtl;
+    }
+    #target {
+      view-timeline: t1 inline;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_inline_vertical_rl_rtl);
+    await assertValueAt(scroller, target, { scrollTop:-50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:-(50 + 20), expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:-(125 + 5), expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:-(200 - 10), expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:-200, expected:-1 });
+  }, 'view-timeline-inset:auto, inline, vertical-rl, rtl');
+</script>
+
+<template id=test_auto_inline_vertical_lr_rtl>
+  <style>
+    #scroller {
+      scroll-padding-inline: 10px 20px;
+      writing-mode: vertical-lr;
+      direction: rtl;
+    }
+    #target {
+      view-timeline: t1 inline;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_inline_vertical_lr_rtl);
+    await assertValueAt(scroller, target, { scrollTop:-50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:-(50 + 20), expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:-(125 + 5), expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:-(200 - 10), expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:-200, expected:-1 });
+  }, 'view-timeline-inset:auto, inline, vertical-lr, rtl');
+</script>
+
+<template id=test_auto_vertical>
+  <style>
+    #scroller {
+      scroll-padding-block: 10px 20px;
+    }
+    #target {
+      view-timeline: t1 vertical;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_vertical);
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset:auto, vertical');
+</script>
+
+<template id=test_auto_vertical_vertical_rl>
+  <style>
+    #scroller {
+      scroll-padding-inline: 10px 20px;
+      writing-mode: vertical-rl;
+    }
+    #target {
+      view-timeline: t1 vertical;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_vertical_vertical_rl);
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset:auto, vertical, vertical-rl');
+</script>
+
+<template id=test_auto_vertical_vertical_rl_rtl>
+  <style>
+    #scroller {
+      scroll-padding-inline: 10px 20px;
+      writing-mode: vertical-rl;
+      direction: rtl;
+    }
+    #target {
+      view-timeline: t1 vertical;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_vertical_vertical_rl_rtl);
+    await assertValueAt(scroller, target, { scrollTop:-50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:-(50 + 20), expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:-(125 + 5), expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:-(200 - 10), expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:-200, expected:-1 });
+  }, 'view-timeline-inset:auto, vertical, vertical-rl, rtl');
+</script>
+
+<template id=test_auto_horizontal>
+  <style>
+    #scroller {
+      scroll-padding-inline: 10px 20px;
+    }
+    #target {
+      view-timeline: t1 horizontal;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_horizontal);
+    await assertValueAt(scroller, target, { scrollLeft:20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollLeft:70 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollLeft:135 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollLeft:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollLeft:200, expected:-1 });
+  }, 'view-timeline-inset:auto, horizontal');
+</script>
+
+<template id=test_auto_horizontal_rtl>
+  <style>
+    #scroller {
+      scroll-padding-inline: 10px 20px;
+      direction: rtl;
+    }
+    #target {
+      view-timeline: t1 horizontal;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_horizontal_rtl);
+    await assertValueAt(scroller, target, { scrollLeft:-20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollLeft:-(70 + 20), expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollLeft:-(135 + 5), expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollLeft:-(200 - 10), expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollLeft:-200, expected:-1 });
+  }, 'view-timeline-inset:auto, horizontal, rtl');
+</script>
+
+<template id=test_auto_horizontal_vertical_lr>
+  <style>
+    #scroller {
+      scroll-padding-block: 10px 20px;
+      writing-mode: vertical-lr;
+    }
+    #target {
+      view-timeline: t1 horizontal;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_horizontal_vertical_lr);
+    await assertValueAt(scroller, target, { scrollLeft:20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollLeft:70 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollLeft:135 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollLeft:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollLeft:200, expected:-1 });
+  }, 'view-timeline-inset:auto, horizontal, vertical-lr');
+</script>
+
+<template id=test_auto_horizontal_vertical_rl>
+  <style>
+    #scroller {
+      scroll-padding-block: 10px 20px;
+      writing-mode: vertical-rl;
+    }
+    #target {
+      view-timeline: t1 horizontal;
+      view-timeline-inset: auto auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_horizontal_vertical_rl);
+    await assertValueAt(scroller, target, { scrollLeft:-20, expected:-1 });
+    await assertValueAt(scroller, target, { scrollLeft:-(70 + 20), expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollLeft:-(135 + 5), expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollLeft:-(200 - 10), expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollLeft:-200, expected:-1 });
+  }, 'view-timeline-inset:auto, horizontal, vertical-rl');
+</script>
+
+<template id=test_auto_mix>
+  <style>
+    #scroller {
+      font-size: 10px;
+      scroll-padding-block: 50px calc(10% + 1em);
+    }
+    #target {
+      view-timeline: t1;
+      view-timeline-inset: 10% auto;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, test_auto_mix);
+    // Note: 10% of scroller height 100px is 10px, and 1em with font-size:10px
+    // is also 10px. Hence we expect the end inset specified as calc(10% + 1em)
+    // to be 20px.
+    await assertValueAt(scroller, target, { scrollTop:50, expected:-1 });
+    await assertValueAt(scroller, target, { scrollTop:50 + 20, expected:0 }); // 0%
+    await assertValueAt(scroller, target, { scrollTop:125 + 5, expected:50 }); // 50%
+    await assertValueAt(scroller, target, { scrollTop:200 - 10, expected:100 }); // 100%
+    await assertValueAt(scroller, target, { scrollTop:200, expected:-1 });
+  }, 'view-timeline-inset:auto, mix');
+</script>
+
+<!--
+  TODO: How to test view-timeline:auto + scroll-padding:auto? The UA may
+  in theory use any value in that case.
+
+  https://drafts.csswg.org/css-scroll-snap-1/#valdef-scroll-padding-auto
+-->
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-inset-computed.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-inset-computed.html
new file mode 100644
index 0000000000..77683a4678
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-inset-computed.html
@@ -0,0 +1,41 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#view-timeline-inset">
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/7243">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+<style>
+  #outer { font-size:10px; }
+  #outer { view-timeline-inset: 1px 2px, auto 3px; }
+  #target { view-timeline-inset: 42px; }
+</style>
+<div id=outer>
+  <div id=target></div>
+</div>
+<script>
+test_computed_value('view-timeline-inset', 'initial', '0px');
+test_computed_value('view-timeline-inset', 'inherit', '1px 2px, auto 3px');
+test_computed_value('view-timeline-inset', 'unset', '0px');
+test_computed_value('view-timeline-inset', 'revert', '0px');
+test_computed_value('view-timeline-inset', '1px');
+test_computed_value('view-timeline-inset', '1%');
+test_computed_value('view-timeline-inset', 'calc(1% + 1px)');
+test_computed_value('view-timeline-inset', '1px 2px');
+test_computed_value('view-timeline-inset', '1px 2em', '1px 20px');
+test_computed_value('view-timeline-inset', 'calc(1px + 1em) 2px', '11px 2px');
+test_computed_value('view-timeline-inset', '1px 2px, 3px 4px');
+test_computed_value('view-timeline-inset', '1px auto, auto 4px');
+test_computed_value('view-timeline-inset', '1px, 2px, 3px');
+test_computed_value('view-timeline-inset', '1px 1px, 2px 3px', '1px, 2px 3px');
+test_computed_value('view-timeline-inset', 'auto auto, auto auto', 'auto, auto');
+
+test(() => {
+  let style = getComputedStyle(document.getElementById('target'));
+  assert_not_equals(Array.from(style).indexOf('view-timeline-inset'), -1);
+}, 'The view-timeline-inset property shows up in CSSStyleDeclaration enumeration');
+
+test(() => {
+  let style = document.getElementById('target').style;
+  assert_not_equals(style.cssText.indexOf('view-timeline-inset'), -1);
+}, 'The view-timeline-inset property shows up in CSSStyleDeclaration.cssText');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-inset-parsing.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-inset-parsing.html
new file mode 100644
index 0000000000..d502b13593
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-inset-parsing.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#view-timeline-inset">
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/7243">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<div id="target"></div>
+<script>
+test_valid_value('view-timeline-inset', 'initial');
+test_valid_value('view-timeline-inset', 'inherit');
+test_valid_value('view-timeline-inset', 'unset');
+test_valid_value('view-timeline-inset', 'revert');
+
+test_valid_value('view-timeline-inset', '1px');
+test_valid_value('view-timeline-inset', '1px 2px');
+test_valid_value('view-timeline-inset', '1px 2em');
+test_valid_value('view-timeline-inset', 'calc(1em + 1px) 2px');
+test_valid_value('view-timeline-inset', '1px 2px, 3px 4px');
+test_valid_value('view-timeline-inset', '1px auto, auto 4px');
+test_valid_value('view-timeline-inset', '1px, 2px, 3px');
+test_valid_value('view-timeline-inset', '1px 1px, 2px 3px', '1px, 2px 3px');
+test_valid_value('view-timeline-inset', 'auto auto, auto auto', 'auto, auto');
+
+test_invalid_value('view-timeline-inset', 'none');
+test_invalid_value('view-timeline-inset', 'foo bar');
+test_invalid_value('view-timeline-inset', '"foo" "bar"');
+test_invalid_value('view-timeline-inset', 'rgb(1, 2, 3)');
+test_invalid_value('view-timeline-inset', '#fefefe');
+test_invalid_value('view-timeline-inset', '1px 2px 3px');
+test_invalid_value('view-timeline-inset', '1px 2px auto');
+test_invalid_value('view-timeline-inset', 'auto 2px 3px');
+test_invalid_value('view-timeline-inset', 'auto auto auto');
+test_invalid_value('view-timeline-inset', '1px / 2px');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-lookup.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-lookup.html
new file mode 100644
index 0000000000..c1797c7ba1
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-lookup.html
@@ -0,0 +1,301 @@
+<!DOCTYPE html>
+<title>Named view-timeline lookup</title>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#view-timelines-named">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { z-index: 0; }
+    to { z-index: 100; }
+  }
+  .scroller {
+    overflow: auto;
+    width: 100px;
+    height: 100px;
+  }
+  .scroller > div {
+    height: 25px;
+    z-index: -1;
+  }
+</style>
+<main id=main></main>
+<script>
+  function inflate(t, template) {
+    t.add_cleanup(() => main.replaceChildren());
+    main.append(template.content.cloneNode(true));
+    main.offsetTop;
+  }
+</script>
+
+<template id=timeline_self>
+  <style>
+    #target {
+      height: 0px;
+      view-timeline: t1;
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div id=target></div>
+    <div></div>
+    <div></div>
+    <div></div>
+    <div></div>
+    <div></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, timeline_self);
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(target).zIndex, '100');
+  }, 'view-timeline on self');
+</script>
+
+<template id=timeline_preceding_sibling>
+  <style>
+    #timeline {
+      height: 0px;
+      view-timeline: t1;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div></div>
+    <div id=timeline></div>
+    <div></div>
+    <div></div>
+    <div id=target></div>
+    <div></div>
+    <div></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, timeline_preceding_sibling);
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(target).zIndex, '75');
+  }, 'view-timeline on preceding sibling');
+</script>
+
+<template id=timeline_ancestor>
+  <style>
+    #timeline {
+      height: 0px;
+      view-timeline: t1;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div></div>
+    <div></div>
+    <div></div>
+    <div id=timeline>
+      <div>
+        <div id=target></div>
+      </div>
+    </div>
+    <div></div>
+    <div></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, timeline_ancestor);
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(target).zIndex, '25');
+  }, 'view-timeline on ancestor');
+</script>
+
+<template id=timeline_ancestor_sibling>
+  <style>
+    #timeline {
+      height: 0px;
+      view-timeline: t1;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div></div>
+    <div id=timeline></div>
+    <div></div>
+    <div>
+      <div>
+        <div id=target></div>
+      </div>
+    </div>
+    <div></div>
+    <div></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, timeline_ancestor_sibling);
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(target).zIndex, '75');
+  }, 'view-timeline on ancestor sibling');
+</script>
+
+<template id=timeline_ancestor_sibling_closest>
+  <style>
+    #timeline1, #timeline2 {
+      height: 0px;
+      view-timeline: t1;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div></div>
+    <div id=timeline1></div>
+    <div></div>
+    <div id=timeline2></div>
+    <div>
+      <div>
+        <div id=target></div>
+      </div>
+    </div>
+    <div></div>
+    <div></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, timeline_ancestor_sibling_closest);
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(target).zIndex, '50');
+  }, 'view-timeline on ancestor sibling, closest wins');
+</script>
+
+<template id=timeline_ancestor_sibling_skips_nonmatching>
+  <style>
+    #timeline1 {
+      height: 0px;
+      view-timeline: t1;
+    }
+    #timeline2 {
+      height: 0px;
+      view-timeline: t2;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div></div>
+    <div id=timeline1></div>
+    <div></div>
+    <div id=timeline2></div>
+    <div>
+      <div>
+        <div id=target></div>
+      </div>
+    </div>
+    <div></div>
+    <div></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, timeline_ancestor_sibling_skips_nonmatching);
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(target).zIndex, '75');
+  }, 'view-timeline on ancestor sibling, skips nonmatching names');
+</script>
+
+<template id=timeline_ancestor_closer_scroll_timeline_wins>
+  <style>
+    #timeline {
+      height: 0px;
+      view-timeline: t1;
+    }
+    #scroll {
+      overflow: auto;
+      scroll-timeline: t1;
+    }
+    #scroll > div {
+      height: 50px;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div></div>
+    <div id=timeline></div>
+    <div></div>
+    <div id=scroll>
+      <div></div>
+    </div>
+    <div>
+      <div>
+        <div id=target></div>
+      </div>
+    </div>
+    <div></div>
+    <div></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, timeline_ancestor_closer_scroll_timeline_wins);
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(target).zIndex, '0');
+  }, 'view-timeline on ancestor sibling, closer scroll-timeline wins');
+</script>
+
+
+<template id=timeline_ancestor_view_timeline_wins_on_same_element>
+  <style>
+    #timelines {
+      height: 0px;
+      view-timeline: t1;
+      scroll-timeline: t1;
+      overflow: auto;
+    }
+    #timelines > div {
+      height: 50px;
+    }
+    #target {
+      animation: anim 1s linear;
+      animation-timeline: t1;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div></div>
+    <div id=timelines>
+      <div></div>
+    </div>
+    <div></div>
+    <div>
+      <div>
+        <div id=target></div>
+      </div>
+    </div>
+    <div></div>
+    <div></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, timeline_ancestor_view_timeline_wins_on_same_element);
+    await waitForNextFrame();
+    assert_equals(getComputedStyle(target).zIndex, '75');
+  }, 'view-timeline on ancestor sibling, view-timeline wins on same element');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-name-computed.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-name-computed.html
new file mode 100644
index 0000000000..5657dc7817
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-name-computed.html
@@ -0,0 +1,36 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#view-timeline-name">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+</head>
+<style>
+  #outer { view-timeline-name: foo, bar; }
+  #target { view-timeline-name: faz; }
+</style>
+<div id=outer>
+  <div id=target></div>
+</div>
+<script>
+test_computed_value('view-timeline-name', 'initial', 'none');
+test_computed_value('view-timeline-name', 'inherit', 'foo, bar');
+test_computed_value('view-timeline-name', 'unset', 'none');
+test_computed_value('view-timeline-name', 'revert', 'none');
+test_computed_value('view-timeline-name', 'none');
+test_computed_value('view-timeline-name', 'foo');
+test_computed_value('view-timeline-name', 'foo, bar');
+test_computed_value('view-timeline-name', 'bar, foo');
+test_computed_value('view-timeline-name', 'a, b, c, D, e');
+test_computed_value('view-timeline-name', 'none, none');
+test_computed_value('view-timeline-name', 'a, b, c, none, d, e');
+
+test(() => {
+  let style = getComputedStyle(document.getElementById('target'));
+  assert_not_equals(Array.from(style).indexOf('view-timeline-name'), -1);
+}, 'The view-timeline-name property shows up in CSSStyleDeclaration enumeration');
+
+test(() => {
+  let style = document.getElementById('target').style;
+  assert_not_equals(style.cssText.indexOf('view-timeline-name'), -1);
+}, 'The view-timeline-name property shows up in CSSStyleDeclaration.cssText');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-name-parsing.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-name-parsing.html
new file mode 100644
index 0000000000..3878d5c583
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-name-parsing.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#view-timeline-name">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<div id="target"></div>
+<script>
+test_valid_value('view-timeline-name', 'initial');
+test_valid_value('view-timeline-name', 'inherit');
+test_valid_value('view-timeline-name', 'unset');
+test_valid_value('view-timeline-name', 'revert');
+
+test_valid_value('view-timeline-name', 'none');
+test_valid_value('view-timeline-name', 'abc');
+test_valid_value('view-timeline-name', '  abc', 'abc');
+test_valid_value('view-timeline-name', 'abc ', 'abc');
+test_valid_value('view-timeline-name', 'aBc');
+test_valid_value('view-timeline-name', 'foo, bar');
+test_valid_value('view-timeline-name', 'bar, foo');
+test_valid_value('view-timeline-name', 'none, none');
+test_valid_value('view-timeline-name', 'a, none, b');
+test_valid_value('view-timeline-name', 'auto');
+
+test_invalid_value('view-timeline-name', 'default');
+test_invalid_value('view-timeline-name', '10px');
+test_invalid_value('view-timeline-name', 'foo bar');
+test_invalid_value('view-timeline-name', '"foo" "bar"');
+test_invalid_value('view-timeline-name', 'rgb(1, 2, 3)');
+test_invalid_value('view-timeline-name', '#fefefe');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-name-tree-scoped.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-name-tree-scoped.html
new file mode 100644
index 0000000000..c216c345ed
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-name-tree-scoped.html
@@ -0,0 +1,145 @@
+<!DOCTYPE html>
+<title>view-timelime-name and tree-scoped references</title>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#view-timelines-named">
+<link rel="help" src="https://drafts.csswg.org/css-scoping-1/#shadow-names">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="/resources/declarative-shadow-dom-polyfill.js"></script>
+
+<main id=main></main>
+<script>
+  function inflate(t, template) {
+    t.add_cleanup(() => main.replaceChildren());
+    main.append(template.content.cloneNode(true));
+    main.offsetTop;
+  }
+
+  setup(() => {
+    polyfill_declarative_shadow_dom(document);
+  });
+</script>
+<style>
+  @keyframes anim {
+    from { z-index: 100; }
+    to { z-index: 100; }
+  }
+</style>
+
+
+<template id=view_timeline_host>
+  <style>
+    .target {
+      animation: anim 10s linear;
+      animation-timeline: timeline;
+    }
+    .scroller > div {
+      view-timeline: timeline horizontal;
+    }
+  </style>
+  <div class=scroller>
+    <div>
+      <div class=target>
+        <template shadowroot=open>
+          <style>
+            :host {
+              view-timeline: timeline vertical;
+            }
+          </style>
+        </template>
+      </div>
+    </div>
+  </div>
+  <style>
+  </style>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, view_timeline_host);
+    let target = main.querySelector('.target');
+    assert_equals(target.getAnimations().length, 1);
+    let anim = target.getAnimations()[0];
+    assert_not_equals(anim.timeline, null);
+    assert_equals(anim.timeline.axis, 'horizontal');
+  }, 'Outer animation can not see view timeline defined by :host');
+</script>
+
+
+<template id=view_timeline_slotted>
+  <style>
+    .target {
+      animation: anim 10s linear;
+      animation-timeline: timeline;
+    }
+    .host {
+      view-timeline: timeline horizontal;
+    }
+  </style>
+  <div class=scroller>
+    <div class=host>
+      <template shadowroot=open>
+        <style>
+          ::slotted(.target) {
+            view-timeline: timeline vertical;
+          }
+        </style>
+        <slot></slot>
+      </template>
+      <div class=target></div>
+    </div>
+  </div>
+  <style>
+  </style>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, view_timeline_slotted);
+    let target = main.querySelector('.target');
+    assert_equals(target.getAnimations().length, 1);
+    let anim = target.getAnimations()[0];
+    assert_not_equals(anim.timeline, null);
+    assert_equals(anim.timeline.axis, 'horizontal');
+  }, 'Outer animation can not see view timeline defined by ::slotted');
+</script>
+
+
+<template id=view_timeline_part>
+  <style>
+    .host {
+      view-timeline: timeline vertical;
+    }
+    .host::part(foo) {
+      view-timeline: timeline horizontal;
+    }
+  </style>
+  <div class=host>
+    <template shadowroot=open>
+      <style>
+          /* Not using 'anim' at document scope, due to https://crbug.com/1334534 */
+          @keyframes anim2 {
+            from { z-index: 100; }
+            to { z-index: 100; }
+          }
+        .target {
+          animation: anim2 10s linear;
+          animation-timeline: timeline;
+        }
+      </style>
+      <div part=foo>
+        <div class=target></div>
+      </div>
+    </template>
+  </div>
+  <style>
+  </style>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, view_timeline_part);
+    let target = main.querySelector('.host').shadowRoot.querySelector('.target');
+    assert_equals(target.getAnimations().length, 1);
+    let anim = target.getAnimations()[0];
+    assert_not_equals(anim.timeline, null);
+    assert_equals(anim.timeline.axis, 'horizontal');
+  }, 'Inner animation can see view timeline defined by ::part');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-shorthand.tentative.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-shorthand.tentative.html
new file mode 100644
index 0000000000..f3efa88c92
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-shorthand.tentative.html
@@ -0,0 +1,104 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.csswg.org/scroll-animations-1/#view-timeline-shorthand">
+<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/7627">
+<link rel="help" href="https://github.com/w3c/csswg-drafts/pull/7694">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/computed-testcommon.js"></script>
+<script src="/css/support/parsing-testcommon.js"></script>
+<script src="/css/support/shorthand-testcommon.js"></script>
+<div id="target"></div>
+<script>
+test_valid_value('view-timeline', 'abcd');
+test_valid_value('view-timeline', 'none block', 'none');
+test_valid_value('view-timeline', 'none inline');
+
+// view-timeline-name: inline/block/horizontal/vertical.
+test_valid_value('view-timeline', 'inline block', 'inline');
+test_valid_value('view-timeline', 'block block', 'block');
+test_valid_value('view-timeline', 'vertical block', 'vertical');
+test_valid_value('view-timeline', 'horizontal block', 'horizontal');
+
+test_valid_value('view-timeline', 'a, b, c');
+test_valid_value('view-timeline', 'a inline, b block, c vertical', 'a inline, b, c vertical');
+test_valid_value('view-timeline', 'auto');
+
+test_invalid_value('view-timeline', 'abc abc');
+test_invalid_value('view-timeline', 'block none');
+test_invalid_value('view-timeline', 'none none');
+test_invalid_value('view-timeline', 'default');
+test_invalid_value('view-timeline', ',');
+test_invalid_value('view-timeline', ',,block,,');
+
+test_computed_value('view-timeline', 'abcd');
+test_computed_value('view-timeline', 'none block', 'none');
+test_computed_value('view-timeline', 'none inline');
+test_computed_value('view-timeline', 'inline block', 'inline');
+test_computed_value('view-timeline', 'block block', 'block');
+test_computed_value('view-timeline', 'vertical block', 'vertical');
+test_computed_value('view-timeline', 'horizontal block', 'horizontal');
+test_computed_value('view-timeline', 'a, b, c');
+test_computed_value('view-timeline', 'a inline, b block, c vertical', 'a inline, b, c vertical');
+
+test_shorthand_value('view-timeline', 'abc vertical',
+{
+  'view-timeline-name': 'abc',
+  'view-timeline-axis': 'vertical',
+});
+test_shorthand_value('view-timeline', 'abc vertical, def',
+{
+  'view-timeline-name': 'abc, def',
+  'view-timeline-axis': 'vertical, block',
+});
+test_shorthand_value('view-timeline', 'abc, def',
+{
+  'view-timeline-name': 'abc, def',
+  'view-timeline-axis': 'block, block',
+});
+test_shorthand_value('view-timeline', 'inline horizontal',
+{
+  'view-timeline-name': 'inline',
+  'view-timeline-axis': 'horizontal',
+});
+
+function test_shorthand_contraction(shorthand, longhands, expected) {
+  let longhands_fmt = Object.entries(longhands).map((e) => `${e[0]}:${e[1]}`).join(';');
+  test((t) => {
+    t.add_cleanup(() => {
+      for (let shorthand of Object.keys(longhands))
+        target.style.removeProperty(shorthand);
+    });
+    for (let [shorthand, value] of Object.entries(longhands))
+      target.style.setProperty(shorthand, value);
+    assert_equals(target.style.getPropertyValue(shorthand), expected, 'Declared value');
+    assert_equals(getComputedStyle(target).getPropertyValue(shorthand), expected, 'Computed value');
+  }, `Shorthand contraction of ${longhands_fmt}`);
+}
+
+test_shorthand_contraction('view-timeline', {
+  'view-timeline-name': 'abc',
+  'view-timeline-axis': 'inline',
+}, 'abc inline');
+
+test_shorthand_contraction('view-timeline', {
+  'view-timeline-name': 'a, b',
+  'view-timeline-axis': 'inline, block',
+}, 'a inline, b');
+
+test_shorthand_contraction('view-timeline', {
+  'view-timeline-name': 'none, none',
+  'view-timeline-axis': 'block, block',
+}, 'none, none');
+
+// Longhands with different lengths:
+
+test_shorthand_contraction('view-timeline', {
+  'view-timeline-name': 'a, b, c',
+  'view-timeline-axis': 'inline, inline',
+}, '');
+
+test_shorthand_contraction('view-timeline', {
+  'view-timeline-name': 'a, b',
+  'view-timeline-axis': 'inline, inline, inline',
+}, '');
+</script>
diff --git a/testing/web-platform/tests/scroll-animations/css/view-timeline-used-values.html b/testing/web-platform/tests/scroll-animations/css/view-timeline-used-values.html
new file mode 100644
index 0000000000..6627eeb998
--- /dev/null
+++ b/testing/web-platform/tests/scroll-animations/css/view-timeline-used-values.html
@@ -0,0 +1,104 @@
+<!DOCTYPE html>
+<title>Used values of view-timeline properties</title>
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#view-timeline-axis">
+<link rel="help" src="https://drafts.csswg.org/scroll-animations-1/#view-timeline-name">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/web-animations/testcommon.js"></script>
+<script src="support/testcommon.js"></script>
+<style>
+  @keyframes anim {
+    from { z-index: 0; }
+    to { z-index: 100; }
+  }
+  .scroller {
+    overflow: hidden;
+    width: 100px;
+    height: 100px;
+  }
+  .scroller > div {
+    width: 300px;
+    height: 300px;
+    z-index: -1;
+  }
+</style>
+<main id=main></main>
+<script>
+  setup(assert_implements_animation_timeline);
+
+  function inflate(t, template) {
+    t.add_cleanup(() => main.replaceChildren());
+    main.append(template.content.cloneNode(true));
+  }
+  async function scrollTop(e, value) {
+    e.scrollTop = value;
+    await waitForNextFrame();
+  }
+  async function scrollLeft(e, value) {
+    e.scrollLeft = value;
+    await waitForNextFrame();
+  }
+</script>
+
+<template id=omitted_axis>
+  <style>
+    #target {
+      view-timeline-name: t1, t2; /* Two items */
+      view-timeline-axis: inline; /* One item */
+      animation: anim 1s linear;
+      animation-timeline: t2;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, omitted_axis);
+    assert_equals(getComputedStyle(target).zIndex, '-1');
+
+    // enter 0% is at scrollTop/Left = -100
+    // exit 100% is at scrollTop/Left = 300
+    // This means that at scrollTop/Left=0, the animation is at 25%.
+
+    await scrollTop(scroller, 0);
+    await scrollLeft(scroller, 0);
+    assert_equals(getComputedStyle(target).zIndex, '25');
+
+    // The timeline should be inline-axis:
+    await scrollTop(scroller, 100); // 50%
+    await scrollLeft(scroller, 40); // 35%
+    assert_equals(getComputedStyle(target).zIndex, '35');
+  }, 'Use the last value from view-timeline-axis if omitted');
+</script>
+
+<template id=omitted_inset>
+  <style>
+    #target {
+      view-timeline-name: t1, t2; /* Two items */
+      view-timeline-inset: 100px; /* One item */
+      animation: anim 1s linear;
+      animation-timeline: t2;
+    }
+  </style>
+  <div id=scroller class=scroller>
+    <div id=target></div>
+  </div>
+</template>
+<script>
+  promise_test(async (t) => {
+    inflate(t, omitted_inset);
+    assert_equals(getComputedStyle(target).zIndex, '-1');
+
+    // 0% is normally at at scrollTop = -100
+    // 100% is normally at scrollTop/Left = 300
+    // However, we have a 100px inset in both ends, which makes the
+    // range [0, 200].
+
+    await scrollTop(scroller, 0);
+    assert_equals(getComputedStyle(target).zIndex, '0');
+    await scrollTop(scroller, 100); // 50%
+    assert_equals(getComputedStyle(target).zIndex, '50');
+  }, 'Use the last value from view-timeline-inset if omitted');
+</script>
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