<!doctype html>
<title>Dynamic evaluation of media queries works fine in presence of empty media rule</title>
<link rel="author" href="mailto:emilio@crisal.io" title="Emilio Cobos Álvarez">
<link rel="author" href="https://mozilla.org" title="Mozilla">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1669600">
<link rel="help" href="https://drafts.csswg.org/mediaqueries-4/">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<iframe width=500 height=300 frameborder=0></iframe>
<script>
let iframe = document.querySelector("iframe");
promise_test(async function (t) {
  await new Promise(resolve => {
    window.addEventListener("load", resolve);
  });
  let frameLoaded = new Promise(resolve => {
    iframe.addEventListener("load", resolve);
  });
  iframe.srcdoc = `
    <style>
      :root { background-color: red; }
      /* This one should never apply */
      @media (min-width: 1500px) {}
      /* This one should change and start matching */
      @media (max-width: 400px) {
        :root { background-color: lime; }
      }
    </style>
  `;
  await frameLoaded;

  function getColor() {
    return iframe.contentWindow.getComputedStyle(iframe.contentDocument.documentElement).backgroundColor;
  }

  assert_equals(getColor(), "rgb(255, 0, 0)", "Should start red");
  iframe.width = 400;
  assert_equals(getColor(), "rgb(0, 255, 0)", "Should turn green");
});
</script>