Backdrop background not global overrides

"@material-ui/core": "^4.9.13"
Not change
```
export default createMuiTheme({
    overrides: {
        MuiBackdrop:{
            root: {
                backgroundColor: 'rgba(255, 0, 0, 0.75)',
            }
        }
})
```
Change
<Modal BackdropProps={{style: {backgroundColor: 'rgba(255, 0, 0, 0.75)'}}}>