title: Polymer 1.0 - Binding css classes
body: <p>I'm trying to include classes based on parameters of a json, so if I have the property color, the $= makes the trick to pass it as a class attribute (based on the polymer <a href="https://www.polymer-project.org/1.0/docs/devguide/data-binding.html#native-binding" rel="noreferrer">documentation</a>)</p>
  
  <pre><code>&lt;div class$="{{color}}"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>The problem is when I'm trying to add that class along an existing set of classes, for instance:</p>
  
  <pre><code>&lt;div class$="avatar {{color}}"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>In that case $= doesn't do the trick. Is any way to accomplish this or each time that I add a class conditionally I have to include the rest of the styles through css selectors instead classes? I know in this example maybe the color could just simple go in the style attribute, it is purely an example to illustrate the problem.</p>
  
  <p>Please, note that this is an issue only in Polymer 1.0.</p>