title: MUI App bar and blur content below fixed Navbar
body: <p>Is there a way to change the background property of my material-ui AppBar component to blur the content blow the fixed navbar?</p>
  <p>I've tried the filter: blur(0) and it doesn't work like I want. I have to get this kind of effect on the navbar with React/Styled-components/Material-UI
  <a href="https://i.stack.imgur.com/vcuSf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vcuSf.png" alt="enter image description here" /></a></p>
  <p>I've searched on the internet for many hours...I want, like in the following link for example, get a blur under this appbar : <a href="https://codesandbox.io/s/mwbwd?file=/demo.js" rel="nofollow noreferrer">https://codesandbox.io/s/mwbwd?file=/demo.js</a></p>