chromium/third_party/blink/web_tests/http/tests/security/mixedContent/insecure-css-in-iframe.html

<html>
<body>
<script>
if (window.testRunner) {
    testRunner.dumpAsText();
    testRunner.overridePreference("WebKitAllowRunningInsecureContent", true);
}
</script>
<p>This test loads a secure iframe that loads an insecure style sheet.
We should trigger a mixed content callback because an active network attacker
can use CSS3 to breach the confidentiality of the HTTPS security origin.</p>
<iframe src="https://127.0.0.1:8443/security/mixedContent/resources/frame-with-insecure-css.html";
></iframe>
</body>
</html>