JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <header>Header</header>
    <div class="content">Content</div>
</div>

CSS

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

.main {
    height: 100%;
    padding-top: 50px;
    box-sizing: border-box;
}

header {
    height: 50px;
    margin-top: -50px;
    width: 100%;
    background-color: #5078a5;
}

.content {
    height: 100%;
    background-color: #999999;
}