JSFiddle - React, Tailwind, and code Playground

HTML

<div id="ifMobile1"> </div>

CSS

#ifMobile1 {
background-image: url('http://st.depositphotos.com/1158045/2720/i/950/depositphotos_27208807-Business.jpg');
width: 500px;
    height: 200px;  
}

@media all and (max-width: 499px) {
    #ifMobile1 {
     background-image: url('http://st.depositphotos.com/1158045/2720/i/950/depositphotos_27208807-Business.jpg')
        width: 300px ;
        height: 100px  ;
    }
}