diff --git a/css/css-pseudo/highlight-cascade-008-ref.html b/css/css-pseudo/highlight-cascade-008-ref.html
new file mode 100644
index 000000000000000..c87ddcf93c9ae7f
--- /dev/null
+++ b/css/css-pseudo/highlight-cascade-008-ref.html
@@ -0,0 +1,18 @@
+<!DOCTYPE html>
+<title>Custom property values from the root element</title>
+<script src="support/selections.js"></script>
+<style>
+  div::selection {
+    background-color: green;
+    text-decoration-line: underline;
+    text-decoration-style: line;
+    text-decoration-thickness: 1px;
+    text-decoration-color: yellow;
+  }
+  span::selection {
+    background-color: blue;
+  }
+</style>
+<div style="width: 300px">PASS if background-color is green when selected, <span>except this which is blue</span>, and underline is yellow.<script>
+  selectNodeContents(document.querySelector("div"));
+</script>
\ No newline at end of file
diff --git a/css/css-pseudo/highlight-cascade-008.html b/css/css-pseudo/highlight-cascade-008.html
new file mode 100644
index 000000000000000..10ca924b8fd1d24
--- /dev/null
+++ b/css/css-pseudo/highlight-cascade-008.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<title>Custom property values from the root element</title>
+<link rel="author" title="Stephen Chenney" href="mailto:schenney@chromium.org">
+<link rel="help" href="https://drafts.csswg.org/css-pseudo-4/#highlight-cascade">
+<link rel="match" href="highlight-cascade-008-ref.html">
+<meta name="assert" value="This test verifies that when a custom property is not found in highlight cascade, its value is taken from the root element.">
+<meta name="fuzzy" content="0-255;0-10">
+<script src="support/selections.js"></script>
+<style>
+  :root {
+    --background-color: green;
+    --decoration-color: purple;
+  }
+  ::selection {
+    --decoration-color: yellow;
+  }
+  div::selection {
+    background-color: var(--background-color, red);
+    text-decoration-line: underline;
+    text-decoration-style: line;
+    text-decoration-color: var(--decoration-color, red);
+  }
+  span::selection {
+    --background-color: blue;
+    background-color: var(--background-color, red);
+  }
+</style>
+<div style="width: 300px">PASS if background-color is green when selected, <span>except this which is blue</span>, and underline is yellow.</div>
+<script>
+  selectNodeContents(document.querySelector("div"));
+</script>
\ No newline at end of file
diff --git a/css/css-pseudo/highlight-cascade-009.html b/css/css-pseudo/highlight-cascade-009.html
new file mode 100644
index 000000000000000..884a0958db0833c
--- /dev/null
+++ b/css/css-pseudo/highlight-cascade-009.html
@@ -0,0 +1,41 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>CSS Pseudo-Elements Test: highlight cascade: inheritance of custom properties</title>
+<link rel="author" title="Stephen Chenney" href="mailto:schenney@chromium.org">
+<link rel="help" href="https://drafts.csswg.org/css-pseudo-4/#highlight-cascade">
+<link rel="help" href="/w3c/csswg-drafts/issues/6641">
+<meta name="assert" content="This test verifies that non-applicable property declarations are ignored in highlight pseudos, that the computed values of ‘font-size’ and ‘line-height’ in highlight pseudos are taken from the originating element, and that ‘text-shadow’ in highlight pseudos respects these values when given ‘em’ and ‘lh’ units.">
+<script src="support/selections.js"></script>
+<link rel="stylesheet" href="support/highlights.css">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+  :root {
+    --background-color: green;
+    --decoration-color: purple;
+  }
+  ::selection {
+    --decoration-color: green;
+  }
+  div::selection {
+    --background-color: blue;
+    background-color: var(--background-color, red);
+  }
+</style>
+<body>
+  <div>Some text</div>
+</body>
+<script>
+    selectNodeContents(document.querySelector("body"));
+
+    const body_selection = getComputedStyle(document.querySelector("body"), "::selection");
+    const div_selection = getComputedStyle(document.querySelector("div"), "::selection");
+    test(() => void assert_equals(body_selection.getPropertyValue("--background-color"), "green"),
+        "body ::selection has the root custom property");
+    test(() => void assert_equals(body_selection.getPropertyValue("--decoration-color"), "green"),
+        "body ::selection uses it's own custom property");
+    test(() => void assert_equals(div_selection.getPropertyValue("--decoration-color"), "green"),
+        "div::selection inherits a custom property");
+    test(() => void assert_equals(div_selection.getPropertyValue("--background-color"), "blue"),
+        "div::selection uses it's own custom property");
+</script>
