JSFiddle - React, Tailwind, and code Playground

HTML

<div class = "main">
            Header
            </div>
            <div class="left">
             Bottom Div
            </div>

CSS

.main {
            width:100%;
            height:60px;
            border: solid;
        }
        
        .left {
         height: 100%;
        width: 300px;
        border:solid;
        }