JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <div id="div1">DIV1</div>
    <div id="div2">DIV2</div>
    <div id="div3">DIV3</div>
    <br style="clear:both;" />
</div>

CSS

div{
    border:1px solid black;
}

#div1{
     float:left; 
    width:100%;
    background-color:red;
}

#div2{
     clear:both;
     float:left;  
    width:50%;
    background-color:green;
}

#div3{
     float:left;
    width:50%;
    background-color:yellow;
}