Роман Александрович

this.handleClick() {
    var element = getElementsByClassName('')
element.setAttribute('background-color ', 'red');
  }

constructor() {
    super();
    
    this.state = { 
flag:false,
 }

  }
this.handleClick() {
    this.setState({
        flag:true
    })
  }
render() {
    return (
      <div className="wrapper">
        <div className="block" backgroundColor={this.state.flag === true ? 'red': 'blue'}>
          <input type="radio" onClick={ this.handleClick } /> 
        </div>
      </div>
    );
  }