title: Add a margin-top to a sibling div on condition that a top sibling has a fixed position
body: <p>The dashboard and content classes are universal in the app (that means they are on every template or page). The header class is only available on certain pages. </p>
  
  <pre><code>&lt;div class="dashboard"&gt;
        &lt;div class="header"&gt;&lt;/div&gt;
        &lt;div class="content"&gt;&lt;/div&gt;
      &lt;/div&gt;
  </code></pre>
  
  <p>What I want is, to add the rule 'fixed position to the header class and fix it to the top of the page on those pages that it exists and give it a white background across the window. Now, when I do that, the content inside the div with content class goes under the header. But, I want that content to have a top margin and be positioned under the header div on only the pages where the header exists.</p>
  
  <p>I know I can add a top padding or margin to the content class, but that will affect all the pages with the content class, but I don't want that to happen?</p>
  
  <p>How can I conditionally achieve this goal?</p>