title: How can I set on hover behaviour for a MUI Button inside a ButtonGroup
body: <p>Using MUI v5, the following code only half works. The first button is colored red (specifically, the border and text are red), however on hover, the color of the border changes to blue (the style is being inherited from the ButtonGroup which is blue by default).</p>
  <p>How can I force the first button to keep its red (from theme.palette.error) border on hover, ideally the 'mui 5' way (ie using sx or emotion or something of this nature)?</p>
  <p>Current behavior: the border and text of the first button are red, but the border becomes blue on hover.</p>
  <p>Desired behavior: the border and text of the first button are always red.</p>
  <p>Any help much appreciated :)</p>
  <pre><code>&lt;ButtonGroup variant=&quot;outlined&quot;&gt;
    &lt;Button color=&quot;error&quot;&gt;
      Again
    &lt;/Button&gt;
    &lt;Button&gt;
      Good
    &lt;/Button&gt;
  &lt;/ButtonGroup&gt;```
  </code></pre>