title: TinyMCE custom format with :before selector
body: <p>I'm trying to setup a custom format in tinyMCE.</p>
  
  <p>I'm trying to make it so that when you select some text and choose this format, it puts a border around the text and uses a <code>:before</code> css selector to prepend an image.</p>
  
  <p><img src="https://i.stack.imgur.com/m0ncA.png" alt="enter image description here"></p>
  
  <p>It seems to be working in Chrome, but not in IE8 or IE9 (Haven't been able to test in other browser versions). In IE8 and 9, the format is applied (the border and changing the text color to red, but the image doesn't appear</p>
  
  <p>Here is my <code>init</code> method</p>
  
  <pre><code>tinymce.init({
      , theme                 : 'modern'
      , selector              : selector
      , entity_encoding       : 'named'
      , plugins               : ['table','contextmenu','paste','fullscreen','image','template','mention']
      , content_css           : contentcss
      , formats               : {
                                    Warning: { inline:'span', 'classes':'rte-warning' }
                                }
      , style_formats         : [
                                  {
                                      title: 'Custom', items: [
                                          { title: 'Warning', format: 'Warning' }
                                      ]
                                  }
                                ]
      , menubar               : false
  });
  </code></pre>
  
  <p>and my css</p>
  
  <pre><code>.rte-warning
  {
      display             : block;
      border              : 1px solid #FD9F08;
      background-color    : #FFFFFF;
      line-height         : 30px;
      padding             : 10px;
      color               : #FC2400;
      font-weight         : bold;
  }
  .rte-warning:before
  {
      content             : "";  /* Empty string must be specified or image doesn't appear for some reason */
      background          : url('/img/rte/Warning.gif');
      display             : block;
      width               : 75px;
      height              : 30px;
      border              : 1px solid #D42E12;
      margin-right        : 10px;
  }
  </code></pre>