Backstage.io MUI button overrides

Question

I want to override the button color on the backstage main panel screens such as Components, Create and API. This worked for rounding corners and font size but not changing color for those buttons (see attached screen shot)

 ...
 MuiButton: {
    styleOverrides: {
      root: ({ theme }) => ({
        borderRadius: 3,
        fontSize: '1rem',
        
      }),
      contained: {
        boxShadow: 'none',       
      },         
    },
  },
   ....