title: Material-Ui theme customization: hover on contained button
body: <p>So I'm trying to configure a theme for Material-Ui on my React app. In the app I use two different type of buttons, contained and outlined. The problem is the hover effect on the contained button (the outlined works fine) and will default to a grey hover effect.</p>
  <pre><code>overrides: {
   MuiButton: {
    contained: {
     backgroundColor: palette.primary.main,
     color: palette.primary.contrastText,
     &quot;&amp;:hover&quot;: {
       backgroundColor: palette.primary.active,
     },
    },
    outlined: {
      color: palette.primary.main,
      &quot;&amp;:hover&quot;: {
        backgroundColor: palette.primary.active,
      },
    },
   }
  }
  </code></pre>
  <p>outlined = working<br />
  contained = not working</p>
  <p>This is from the element inspector, where my color is the one with a strike through <br />
  <strong>background-color:</strong><br />
  #e0e0e0.MuiButton-contained:hover<br>
  <strike>rgba(23, 0, 255, 0.3).MuiButton-contained:hover</strike></p>
  <p>Anyone got any idea what's wrong?</p>