1 files changed, 55 insertions, 0 deletions
diff --git a/testing/web-platform/tests/html/semantics/interactive-elements/the-dialog-element/backdrop-descendant-selector.html b/testing/web-platform/tests/html/semantics/interactive-elements/the-dialog-element/backdrop-descendant-selector.html
new file mode 100644
index 0000000000..73706548ea
--- /dev/null
+++ b/testing/web-platform/tests/html/semantics/interactive-elements/the-dialog-element/backdrop-descendant-selector.html
@@ -0,0 +1,55 @@
+<!DOCTYPE html>
+<html>
+<head>
+<link rel="match" href="backdrop-descendant-selector-ref.html">
+<link rel="help" href="https://fullscreen.spec.whatwg.org/#new-stacking-layer">
+<style>
+dialog {
+    visibility: hidden;
+}
+
+::backdrop {
+    visibility: visible;
+    position: absolute;
+    height: 100px;
+    width: 100px;
+    background: red;
+}
+
+/* This shouldn't be matched, dialog is not the parent of ::backdrop.
+ * It is given high specificity so we actually test something.
+ */
+#dialog-parent > #dialog > ::backdrop,
+#dialog-parent > #dialog ::backdrop {
+    background: red;
+}
+
+#dialog-parent > ::backdrop {
+    top: 100px;
+    left: 100px;
+    background: green;
+}
+
+#backdrop-ancestor ::backdrop {
+    top: 100px;
+    left: 300px;
+    background: green;
+}
+</style>
+</head>
+<body>
+Test ::backdrop used in descendant selectors. The test passes if there are two green boxes and no red.
+
+<div id="dialog-parent">
+    <dialog id="dialog"></dialog>
+</div>
+<div id="backdrop-ancestor">
+    <p><span><dialog></dialog></span></p>
+</div>
+<script>
+var dialogs = document.querySelectorAll('dialog');
+for (var i = 0; i < dialogs.length; ++i)
+    dialogs[i].showModal();
+</script>
+</body>
+</html>