JSFiddle - React, Tailwind, and code Playground

HTML

<div class="layout">
    <div class="header">header</div>
    <div class="content">content</div>
</div>

CSS

html, body {
    height: 100%;
    margin: 0;
}

.layout {
    display: table;
    
    width: 100%;
    height: 100%;
}

.header {
    display: table-row; 
    
    height: 100px;    
    background: #ddd;
}

.content {
    display: table-cell;
    
    background: #777;
}