JSFiddle - React, Tailwind, and code Playground

HTML

<div id="header"></div>
<div id="fill-the-fold">
    <div id="content">

    </div>
</div>

CSS

html,body{ margin:0px; height:100%;} 
div{
    box-sizing: border-box;
}
#header {
    border: 1px solid green;
    width: 100%;
    height: 100px;
}

#fill-the-fold {
    margin-top: -100px;
    padding-top: 100px;
    height: 100%;
}

#content{
    border: 1px solid red;
    height: 100%;
}