JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div class="block">
        <div id="header" class="content">Header</div>
    </div>
    <div class="block">
        <div id="section" class="content">Section</div>
    </div>
</div

CSS

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

#container {
    display: table;
    width: 100%;
    height: 100%;
    border:5px yellow;
}

.block {
    display: table-row;
}

.content {
    display: table-cell;
    border: 1px solid red;
}

#header {
    height: 250px;
}