JSFiddle - React, Tailwind, and code Playground

HTML

<div id="header">Header</div>
<div id="container">
    <div id="right">Right</div>
    <div id="left">Left</div>   
</div>

CSS

div #container{
    width:100%;
    height:500px;
}
div#header {
    height:70px;
    border:1px solid;
}
div#left {
    width:200px;
    height:500px;
    float:left;
    background-color:green;
    
}
div#right {
    width:calc(100% - 200px);
    width: -webkit-calc(100% - 200px);
    width: -moz-calc(100% - 200px);
    height:500px;
    float:right;
   background-color:red;
}