title: Material-ui style dialog / modal backdrop
body: <p>How do I go about styling the transparent dark overlay of a material-ui dialog or modal?
  I'm using material-ui/React/Typescript.</p>
  
  <p><a href="https://i.stack.imgur.com/ODQvN.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ODQvN.png" alt="enter image description here"></a></p>
  
  <p>Instead of a transparent dark, I want it to be a transparent white.
  I'd prefer a <a href="https://cssinjs.org" rel="noreferrer">JSS</a> solution but an inline style is welcomed.</p>