1 files changed, 141 insertions, 0 deletions
diff --git a/testing/web-platform/tests/css/css-anchor-position/position-try-cascade.html b/testing/web-platform/tests/css/css-anchor-position/position-try-cascade.html
new file mode 100644
index 0000000000..d73ddd586a
--- /dev/null
+++ b/testing/web-platform/tests/css/css-anchor-position/position-try-cascade.html
@@ -0,0 +1,141 @@
+<!DOCTYPE html>
+<title>CSS Anchor Positioning Test: @position-try and cascade interaction</title>
+<link rel="help" href="https://drafts.csswg.org/css-anchor-position-1/#fallback-apply">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+  .cb {
+    position: relative;
+    width: 100px;
+    height: 100px;
+    background: lightpink;
+    display: inline-block;
+  }
+  .abs {
+    position: absolute;
+    background: darkcyan;
+    left: 0px;
+    top: 0px;
+    width: 150px; /* force fallback */
+    height: 25px;
+    position-try-options: --pf;
+  }
+  @position-try --pf {
+    width: 50px;
+    left: 50px;
+    top: 50px;
+  }
+</style>
+
+<!-- Basic @position-try rule -->
+<div class=cb>
+  <div id=abs_try class=abs></div>
+</div>
+<script>
+  test(() => {
+    assert_equals(abs_try.offsetLeft, 50);
+    assert_equals(abs_try.offsetTop, 50);
+  }, '@position-try rule applies');
+</script>
+
+<!-- Inline style -->
+<div class=cb>
+  <div id=abs_inline class=abs style="left:20px"></div>
+</div>
+<script>
+  test(() => {
+    assert_equals(abs_inline.offsetLeft, 50);
+    assert_equals(abs_inline.offsetTop, 50);
+  }, '@position-try rule wins over inline style');
+</script>
+
+<!-- !important -->
+<style>
+  #abs_important {
+    left: 10px !important;
+  }
+</style>
+<div class=cb>
+  <div id=abs_important class=abs></div>
+</div>
+<script>
+  test(() => {
+    assert_equals(abs_important.offsetLeft, 10);
+    assert_equals(abs_important.offsetTop, 50);
+  }, '@position-try rule does not win over !important');
+</script>
+
+<!-- Animations -->
+<style>
+  @keyframes anim {
+    from { top: 20px; }
+    to { top: 20px; }
+  }
+  #abs_animation {
+    animation: anim 1000s steps(2, start) paused;
+  }
+</style>
+<div class=cb>
+  <div id=abs_animation class=abs></div>
+</div>
+<script>
+  test(() => {
+    assert_equals(abs_animation.offsetLeft, 50);
+    assert_equals(abs_animation.offsetTop, 20);
+  }, '@position-try rule does not win over animations');
+</script>
+
+<!-- Transitions -->
+<style>
+  #abs_transition.move {
+    top: 10px !important;
+    transition: top 1000s steps(2, start);
+</style>
+<div class=cb>
+  <div id=abs_transition class=abs></div>
+</div>
+<script>
+  test(() => {
+    abs_transition.offsetTop;
+    abs_transition.classList.add('move');
+    assert_equals(abs_transition.offsetLeft, 50);
+    assert_equals(abs_transition.offsetTop, 30);
+  }, '@position-try rule does not win over transitions');
+</script>
+
+<!-- revert / revert-layer -->
+<style>
+  #abs_revert {
+    position-try-options: --pf-revert;
+  }
+  @layer author-layer {
+    #abs_revert {
+      top: 30px;
+      left: 30px;
+    }
+  }
+  #abs_revert {
+    top: 20px;
+    left: 20px;
+    /* overflowing .cb to force --pf-revert to be applied */
+    width: 200px;
+    height: 200px;
+  }
+  @position-try --pf-revert {
+    left: revert;
+    top: revert-layer;
+    width: 30px;
+    height: 30px;
+  }
+</style>
+<div class=cb class=abs>
+  <div id=abs_revert class=abs></div>
+</div>
+<script>
+  test(() => {
+    assert_equals(abs_revert.offsetLeft, 0, "left reverted back to user origin");
+    assert_equals(abs_revert.offsetTop, 20, "top reverted back to author");
+    assert_equals(abs_revert.offsetWidth, 30, "width from --pf-revert");
+    assert_equals(abs_revert.offsetHeight, 30, "height from --pf-revert");
+  }, '@position-try revert / revert-layer reverts to user / author origin');
+</script>