title: Adding pixels in css
body: <p>is there any ways to make class add pixels to element?
  For example: </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.block {
    height: 100px;
    width: 100px;
    background-color: red
  }
  
  .wider {
    width: calc(width + 100px);
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="block wider"&gt;&lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>So, .wider makes .block elements wider on 100px, how do I do that in the right way?</p>