Is your feature request related to a problem? Please describe.
I want to use variables values in @global
but if @global is a function then "Uncaught TypeError: Cannot set property 'fnStyle1587427462315' of null", if fields of @global are functions they are ignored

const useStyles = createUseStyles({
  '@global':  {
    '#sntch_block': {
      display: () => 'none',
    },
  },
});

Describe the solution you'd like
Variables values like already implemented but working inside @global

Are you willing to implement it?
Yes if it's simple to do (your code seems so clean and easy to understand)
I have updated from early 10 version to the latest (react-jss and jss 10.1.1, I first only updated react-jss to 10.1.1 and let jss in 10.0.1 which triggers an error "sheet.updateOne" is not a function, you should consider printing a warning when incompatible version are being run together because it is hard otherwise to debug what is wrong). And both of these version have this issue.