<!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>
  #outer {
    border: 10px solid transparent;
  }

  #inner {
    border: 10px solid;
  }
</style>
<div id="outer"><div id="inner"></div></div>
