JSFiddle - React, Tailwind, and code Playground

HTML

<div id="div1" ></div>
<div id="div2" ></div>
<div id="div3"></div>

CSS

#div1, #div2, #div3 {
    float:left;
    height:200px;
}
#div1 {
    background-color:red;
    width:40%;
}
#div2 {
    background-color:yellow;
    width:40%;
}
#div3 {
    background-color:green;
    width:20%;
}

@media (max-width: 600px) {
    #div1, #div2, #div3 {width:100%;}
  }