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<!DOCTYPE HTML>
<title>CSS Shadow Parts - :host::part() cascading</title>
<link rel="help" href="https://drafts.csswg.org/css-shadow-1/#part">
<link rel="help" href="https://drafts.csswg.org/css-shadow-1/#host-selector">
<link rel="help" href="https://drafts.csswg.org/css-cascade-5/#cascade-sort">
<link rel="help" href="https://drafts.csswg.org/selectors-4/#specificity">
<link rel="author" title="L. David Baron" href="https://dbaron.org/">
<link rel="author" title="Google" href="http://www.google.com/">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id="host"></div>
<script>
test(function() {
let host = document.getElementById("host");
let shadow = host.attachShadow({mode: "open"});
// Make three rules with equal specificity, so that they cascade by
// order. Pseudo-elements and elements have the same specificity.
// Pseudo-classes and attribute selectors have the same specificity.
shadow.innerHTML = `
<style>
div[part="part-name"] {
color: red;
}
:host::part(part-name) {
color: lime;
background-color: red;
}
div[part="part-name"] {
background-color: green;
}
</style>
<div part="part-name"></div>
`;
let part_cs = getComputedStyle(shadow.querySelector('div[part="part-name"]'));
assert_equals(part_cs.color, "rgb(0, 255, 0)",
":host::part() selectors override earlier selectors with " +
"same encapsulation context and specificity");
assert_equals(part_cs.backgroundColor, "rgb(0, 128, 0)",
":host::part() selectors are overridden by later selectors " +
"with same encapsulation context and specificity");
}, ":host::part has correct cascading behavior");
</script>
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