title: How to change the hover state for CardActionArea / ButtonBase
body: <p>I'm currently using the CardActionArea / ButtonBase Material Ui @next components for my app. </p>
  
  <p>I can't seem to change the onhover effect that comes with the button. </p>
  
  <p>I also can't seem to find the selector that is causing the background overlay color on hover. Can anyone help with this?</p>
  
  <p><a href="https://material-ui.com/api/card-action-area/" rel="nofollow noreferrer">https://material-ui.com/api/card-action-area/</a></p>
  
  <p><a href="https://material-ui.com/api/button-base/" rel="nofollow noreferrer">https://material-ui.com/api/button-base/</a> </p>
  
  <p>I've tried setting a backgroundColour in the className prop, classes prop (applied to <code>root</code>/<code>focusVisible</code>/<code>focusHighlight</code>) but with no luck.</p>
  
  <p>Demo that might better explain what I'm trying to do: <a href="https://codesandbox.io/s/jnnr5wo029" rel="nofollow noreferrer">https://codesandbox.io/s/jnnr5wo029</a></p>
  
  <p>Expected result: onHover style would be overridden / disabled with css</p>
  
  <p>Actual result: Grey onHover style is still applied</p>