title: HTML+CSS. How do I place a horizontal line atop a button?
body: <p>I am an iOS and 3D dev taking on some Web dev work. In HTML/CSS/JS I have found it impossible to do something that I assumed was trivial: place a horizontal line atop a button.</p>
  
  <p>Here is my button with a background image:</p>
  
  <pre><code>&lt;button id="myButton" style="background-image: url(assets/cursor-filter-thumbnail.png);" class="igv-filter-button" data-toggle="modal" data-target="#myDataTarget"&gt;
  &lt;/button&gt;
  </code></pre>
  
  <p>Here is the CSS:</p>
  
  <pre><code>.igv-filter-button {
      position: absolute;
      width: 128px;
      border:none;
      padding: 0;
      height: 100%;
      background: none;
  }
  </code></pre>
  
  <p>Now I want to place a horizontal line atop this button that I will programmatically move up/down using JS. Can someone place enlighten me?</p>