JSFiddle - React, Tailwind, and code Playground

HTML

<div id='container'>
    <div id='left'>
        &nbsp;
    </div>
    <div id='right'>
        &nbsp;
    </div>
</div>

CSS

#container,#left,#right{
    margin: 0;padding:0;
}
#container{font-size : 0}
#left{
    display : inline-block;
    width : 50%;
    background : #00bbbb;
    font-size: 19px
    
}

@media (max-width: 400px) {#left {width: 100%;}}


#right{
    display : inline-block;
    width : 50%;
    background: #eee;
    font-size: 19px
}