css/css-position/position-fixed-root-element-grid.html

<!DOCTYPE html>
<html>
  <meta charset="UTF-8">
  <title>CSS Position: Box inset properties & position:fixed grid container as the root element</title>
  <link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com"/>
  <link rel="author" title="Ting-Yu Lin" href="mailto:tlin@mozilla.com">
  <link rel="author" title="Mozilla" href="http://www.mozilla.org/">
  <link rel="help" href="https://drafts.csswg.org/css-position-3/#insets">
  <link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1584890">
  <link rel="match" href="position-fixed-root-element-ref.html">
  <meta name="assert" content="This test verifies the box inset properties on a position:fixed grid container root element.">

  <style>
  html {
    display: grid;
    position: fixed;
    left: 10px;
    right: 20px;
    top: 30px;
    bottom: 40px;
    border: 5px dashed black;
    box-sizing: border-box;
  }
  </style>

  The black border should encompass the whole viewport,
  with a bit of space on each side.
  <br><br>
  It shouldn't just shrinkwrap this text's height.
</html>