using theme.spacing inside theme definition

I have the following theme setup:

export const themeDefault = createTheme({
  themeName: 'Default (Mortgage Hub)',
  spacing: 4,
  ...typography,
  palette,
  components: {
    MuiButton: {
      styleOverrides: {
        root: {
          paddingLeft: theme.spacing(12),
          paddingRight: theme.spacing(4),
          border: '10px',
        },
      },
    },
  },
})

And I would like to use theme.spacing inside however, of course. Theme is not defined yet. I have tried to use makeStyles & useTheme however these are hooks. So of course they will not work.

Are you able to supply styleOverrides once the theme has been indicated?