title: inherit width doesn't work with percentage value
body: <p>I have 2 <code>div</code>s. The parent <code>div</code> has <code>relative</code> position and the child <code>div</code> has <code>fixed</code> position.</p>
  
  <p>If I use a flat amount of <code>width</code> on the parent <code>div</code>, <code>width: inherit;</code> works perfectly.
  When I use <code>width: 100%;</code> on the parent <code>div</code>, child <code>div</code> has more <code>width</code> than its parent.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>*,
  *::before,
  *::after {
    box-sizing: border-box;
  }
  .content {
    position: relative;
    background: black;
    width: 100%;
  }
  .fixedElement {
    position: fixed;
    width: inherit;
    background: yellow;
    z-index: 2;
    top: 0px;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="content"&gt;
    parent
    &lt;div class="fixedElement"&gt;
      child
    &lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p><a href="https://jsfiddle.net/537yzrpy/14/" rel="nofollow">Fiddle </a></p>
  
  <p>Am I missing something here?</p>
  
  <p>I'm thinking of using <code>jQuery</code> to set the <code>width</code> of the child but I'm sure it's not a good solution as it could be solved only with <code>css</code>.</p>