how to give theme background in material ui selector code example

Example: use theme in class component material ui

import { withStyles } from "@material-ui/core/styles";

const styles = theme => ({
  root: {
    backgroundColor: "red"
  }
});

class ClassComponent extends Component {
  state = {
    searchNodes: ""
  };

  render() {
    const { classes } = this.props;
    return (
      <div className={classes.root}>Hello!</div>
    );
  }
}

export default withStyles(styles, { withTheme: true })(ClassComponent);