<!doctype html>
<title>CSS Test Reference.</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<link rel="author" title="Mozilla" href="https://mozilla.org">
<style>
  * {
    margin: 0;
    padding: 0;
  }

  :root, #outer {
    width: 100vw;
    height: 100vh;
    overflow: hidden;
  }

  #outer {
    transform-origin: 0 0;
    transform: scale(5);
  }

  #pad {
    /* So that scaling by five it takes half of the viewport */
    height: 10vh;
  }

  #filtered {
    width: 100%;
    height: 10vh;
    background: green;
  }
</style>
<div id="outer">
  <div id="pad"></div>
  <div id="filtered"></div>
</div>
