how to custmizing css in material ui code example

Example 1: how to use css in material ui

import React from 'react';
import Button from '@material-ui/core/Button';
import './PlainCssButton.css';

export default function PlainCssButton() {
  return (
    <div>
      <Button>Default</Button>
      <Button className="button">Customized</Button>
    </div>
  );
}

Example 2: how to use css in material ui

<Button
  classes={{
    root: classes.root, // class name, e.g. `classes-nesting-root-x`
    label: classes.label, // class name, e.g. `classes-nesting-label-x`
  }}
>
  classes nesting
</Button>