title: How to add div banner before every page content using JS?
body: <p>For example, there is the following page:</p>
  
  <pre><code>&lt;html&gt;
    &lt;head&gt;
      &lt;style&gt;
        .a {
          background-color: red;
        }
        .b {
          background-color: yellow;
        }
      &lt;/style&gt;
    &lt;/head&gt;
    &lt;body&gt;
  
      &lt;div class="a"&gt;123&lt;/div&gt;
  
      &lt;div&gt;456&lt;/div&gt;
  
      &lt;script&gt;
        var banner = document.createElement("div");
        banner.className = "b";
        banner.innerHTML = "Banner Content";
  
        var content = document.getElementsByClassName("a")[0];
        content.parentNode.insertBefore(banner, content);
      &lt;/script&gt;
    &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>
  
  <p>As you can see, I just add 'banner' div before first page item. But this code isn't universal; if items are absolute positioned, my code doesn't work. I need to create some JS which will add 'banner' div before page content for every situation. Is it possible? Thanks in advance!</p>