问如何在reactJS中设置背景图像的属性

EN

//App.js
import React from "react";
import NavBar from "./NavBar";

const ContactUs = () => {
    return(
        <div className="contactUsContainer">
            <NavBar/>
            <div className="contactUsHeader">
                <h2>Contact Us</h2>
            </div>
            <div>
                <span></span>
            </div>
        </div>
    );
}

export default ContactUs;


//app.css

.contactUsContainer {
  height: 100%;
  width: 100%
}

.contactUsHeader {
  display: flex;
  flex-direction: column;
  align-items: center;
  background-image: url("http://www.stapl.co.in/sites/default/files/imagecache/full-zoom/files/projects/6/83/6-83-wartsilla-3.jpg");
  background-repeat: no-repeat;
  background-size: cover;
  height:30vh;
  width: 100vw;
  background-color: blue

}