diff --git a/src/transparency-iframe.html b/src/transparency-iframe.html
new file mode 100644
index 0000000..8ffc963
--- /dev/null
+++ b/src/transparency-iframe.html
@@ -0,0 +1,18 @@
+<!doctype html>
+<html>
+<head>
+<title>Minimal transparent page</title>
+<style>
+  html, body {
+    margin: 0; padding: 0;
+    background: transparent !important;
+    font: 14px system-ui, sans-serif;
+    color: #000;
+  }
+  div { padding: 8px; }
+</style>
+</head>
+<body>
+<div>Minimal page on localhost:8000.<br>If the parent's magenta backdrop shows through, cross-origin iframe transparency works in this browser.</div>
+</body>
+</html>