at-supports-selector-file-selector-button.html

<!doctype html>
<html>
  <head>
    <title>CSS Test (Conditional Rules): In @supports, ::file-selector-button can be parsed successfully</title>
    <link rel="author" title="Tim Nguyen" href="https://github.com/nt1m">
    <link rel="help" href="https://drafts.csswg.org/css-conditional-3/#at-supports">
    <link rel="help" href="https://drafts.csswg.org/css-pseudo/#file-selector-button-pseudo">
    <link rel="match" href="at-supports-001-ref.html">
    <style>
      div {
        background: red;
        height: 100px;
        width: 100px;
      }
      @supports selector(input::file-selector-button) {
        div { background-color:green; }
      }
    </style>
  </head>
  <body>
    <p>Test passes if there is a <strong>filled green square</strong> and <strong>no red</strong>.</p>
    <div></div>
  </body>
</html>

chromium/third_party/blink/web_tests/external/wpt/css/css-conditional/at-supports-selector-file-selector-button.html