Untitled

dabblet.css

html {
  height: 100%;
}

body {
  height: 100%;
  border: solid 20px blue;
}

div.red {
  height: 100%;
  border: solid 20px #800;
}

div.green {
  height: 0;
  border: solid 20px green;
}

dabblet.html

<div class='red'>
  <div class='green'>&nbsp;</div>
</div>

settings.json

{"view":"split","fontsize":"100","seethrough":"","prefixfree":"1","page":"css"}