JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <div class="menu">1</div>
    <div class="menu">2</div>
    <div class="content">3</div>
    
</div>

CSS

body > div {
    background: lightgreen;
    width: 600px
        height:600px;
    overflow: auto;
}

.menu{
    background: lightyellow;
    float: left;
}

.content{
    background:red;
    
}