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+<!DOCTYPE HTML>
+<!--
+  Tests that setting a fixed top margin in the compositor results
+  in the margin being applied to an element sticky to the top.
+
+  The fixed margin is specified as a test-pref in reftest.list.
+
+  The purpose of the fixed margin is to compensate for the transform that the
+  dynamic toolbar applies to the entire content area. We don't have a way of
+  simulating that transform in a reftest, so the fixed margin in isolation will
+  cause the fixed element to be offset from the top of the screen.
+-->
+<html>
+<meta name="viewport" content="width=device-width">
+<style>
+html {
+    scrollbar-width: none;
+}
+#scrolled {
+    display: flex;
+    justify-content: space-around;
+    align-items: flex-start;
+
+    height: 2000px;
+    width: 100%;
+}
+#sticky {
+    width: 100%;
+    height: 200px;
+    position: sticky;
+    top: 20px;
+    background: red;
+}
+</style>
+<body>
+  <div id="scrolled">
+    <div id="sticky"></div>
+  </div>
+</body>
+</html>