title: How do I use material-ui themed error style (color) for non-form text
body: <p>The docs are clear on using error styles for form inputs such as text fields. But how do I use the same style on a custom element such as a text label for a <a href="https://material-ui.com/demos/buttons/#contained-buttons" rel="nofollow noreferrer">file upload button</a>, or any other custom component that might not fit the a pre-defined component?</p>
  
  <p>Edit for clarity: I don't want to just choose a color I like and plop it in my css with an appropriate selector. I want to make sure I'm using the same error color as the theme, whether that's the default, some imported theme, or custom (if custom it's pretty easy, but not DRY, to just use the same value in css).</p>
  
  <p>Specifically, in this use case, I want to limit users to uploading files less than 100MB, and display an error message if they have selected a file larger than this limit. I'd like to display the text in the error style of the configured theme, but from the material-ui docs I can only see how to set error properties of pre-packaged components such as text fields.</p>
  
  <p>So here I have, simplified:</p>
  
  <pre><code>      &lt;input
          accept="video/*"
          id="file-upload-button"
          type="file"
          onChange={(e) =&gt; {this.fileChanged(e);}}
        /&gt;
        &lt;label htmlFor="file-upload-button"&gt;
          &lt;Button variant="contained" component="span" color="default"&gt;
            Browse video
          &lt;/Button&gt;
          &lt;br /&gt;&lt;small&gt;(Max size: 100MB)&lt;/small&gt;
        &lt;/label&gt;
  </code></pre>
  
  <p>where the <code>input</code> tag has <code>display: none</code> applied via a css file. Also,</p>
  
  <pre><code>  fileChanged(e) {
      let file = e.target.files[0];
      let sizeMB = file.size / 2**20;
      this.setState({
        selectedFile: e.target.files[0],
        fileTooLarge: sizeMB &gt; 100
      });
    }
  </code></pre>
  
  <p>How do I get the theme's error color to apply it to the "Max Size" message or other element?</p>