title: How to change Polymer(1.0) paper-toolbar background colour?
body: <p>Yesterday I decided to try Polymer 1.0 and I'm already facing difficulties when trying to styling the paper-toolbar.</p>
  
  <p>The documentation says that the background colour can be changed by using:
  --paper-toolbar-background</p>
  
  <p>But how can I use it on CSS?</p>
  
  <p>I tried the following:</p>
  
  <pre><code>    paper-toolbar {
          --paper-toolbar-background: #e5e5e5;
      }
  </code></pre>
  
  <p>Also this:</p>
  
  <pre><code>    paper-toolbar {
          --paper-toolbar {
              background: #e5e5e5;
          }
      }
  </code></pre>
  
  <p>But neither worked. What is the correct way to do it?</p>
  
  <p>Thanks.</p>