JSFiddle - React, Tailwind, and code Playground

HTML

<div class="header">
    Header
</div>
<div class="main">
    <span class="leftnav">
        <div class="lefttop">
            lefttop
        </div>
        <div class="leftbottom">
            leftbottom
        </div>
    </span>
    <span class="rightside">
        <div class="righttop">
            righttop
        </div>
        <div class="rightbottom">
            rightbottom
        </div>
    </span>
</div>

CSS

div, span {
    border-width: 1px;
    border-style: solid;
    border-color: black;
}