title: Overriding Card titleStyle and subtitleStyle not working in material-ui
body: <p>I have to apply different styles for title and subtitle elements of Card components using Material-ui.</p>
  
  <p>Following is my code:</p>
  
  <pre><code>const mediaTitleStyles = {
    ....
    ....
    title:{
      fontSize: 35,
      fontWeight: 'bold',
    },
    subtitle:{
      fontSize: 25,
      fontWeight: 'bold',
    },
  
  };
  
  &lt;Card&gt;
  
      &lt;CardMedia style={{background: '#9E9E9E'}}
       overlay={&lt;CardTitle title="LIVE THE LANGUAGE" subtitle="Learn a language based on the situations that are relevant to you." /&gt;}
       overlayContentStyle={mediaTitleStyles.content}
       titleStyle = {mediaTitleStyles.title} subtitleStyle={mediaTitleStyles.subtitle}
      &gt;
      .................
  </code></pre>
  
  <p>Basically, I am trying to apply different font-size for those two elements. But, the output is not working? Do I have to include anything?</p>