diff --git a/css/css-position/overlay/overlay-transition-backdrop-entry.html b/css/css-position/overlay/overlay-transition-backdrop-entry.html
new file mode 100644
index 00000000000000..e8e8ab353ad441
--- /dev/null
+++ b/css/css-position/overlay/overlay-transition-backdrop-entry.html
@@ -0,0 +1,23 @@
+3<!DOCTYPE html>
+<title>CSS Position Test: overlay transition with ::backdrop during entry animation</title>
+<link rel="help" href="https://drafts.csswg.org/css-position-4/#overlay">
+<link rel="match" href="green-ref.html">
+<style>
+  body {
+    background-color: green;
+  }
+  [popover] {
+    display: block;
+    visibility: hidden;
+    transition-delay: 60s;
+    transition-property: overlay;
+    transition-duration: 60s;
+  }
+  [popover]::backdrop {
+    background-color: blue;
+  }
+</style>
+<div popover id="foo"></div>
+<script>
+  foo.showPopover();
+</script>
diff --git a/css/css-position/overlay/overlay-transition-backdrop.html b/css/css-position/overlay/overlay-transition-backdrop.html
new file mode 100644
index 00000000000000..7b5a553933d7e1
--- /dev/null
+++ b/css/css-position/overlay/overlay-transition-backdrop.html
@@ -0,0 +1,19 @@
+3<!DOCTYPE html>
+<title>CSS Position Test: overlay transition with ::backdrop</title>
+<link rel="help" href="https://drafts.csswg.org/css-position-4/#overlay">
+<link rel="match" href="green-ref.html">
+<style>
+  [popover] {
+    display: block;
+    visibility: hidden;
+    transition: overlay 60s step-end;
+  }
+  [popover]::backdrop {
+    background-color: green;
+  }
+</style>
+<div popover id="foo"></div>
+<script>
+  foo.showPopover();
+  foo.hidePopover();
+</script>
