How to change the border color of MUI TextField

<CssTextField
  label="Username"
  className="username"
  name="username"
  onChange={this.onChange}
  type="text"
  autoComplete="current-password"
  margin="normal"
  inputProps={{ style: { fontFamily: 'nunito', color: 'white' } }}
/>

//declare the const and add the material UI style
const CssTextField = withStyles({
  root: {
    '& label.Mui-focused': {
      color: 'white',
    },
    '& .MuiInput-underline:after': {
      borderBottomColor: 'yellow',
    },
    '& .MuiOutlinedInput-root': {
      '& fieldset': {
        borderColor: 'white',
      },
      '&:hover fieldset': {
        borderColor: 'white',
      },
      '&.Mui-focused fieldset': {
        borderColor: 'yellow',
      },
    },
  },
})(TextField);