title: Edge evaluates @supports(mask) as true when mask isn't supported
body: <p>Edge doesn't support <a href="https://caniuse.com/#search=mask" rel="noreferrer">CSS mask</a>, yet the <code>@supports</code> statement below is calculating as <code>true</code> and the enclosed styles are being applied in Edge. What can I put into the <code>@supports</code> argument to get Edge to ignore the conditional block</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>body {
    font-family: monospaced;
    color: red;
    background-image: url(test.png);
  }
  
  @supports(mask: url("")) {
    body {
      background-color: #eee;
      font-family: sans-serif;
      color: rebeccapurple;
      mask: url(test.svg);
      mask-size: cover;
    }
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;h3&gt;This should be red and mono-spaced in Edge&lt;/h3&gt;</code></pre>
  </div>
  </div>
  </p>