JSFiddle - React, Tailwind, and code Playground

HTML

<div class='container'>
    <div class='horiz'></div>
    <div class='vert'></div>
</div>

CSS

.container {
    width:320px;
    height:320px;
    border:solid 5px green;
    overflow-x: hidden;
}
.horiz{
    width:500px;
    height:30px;
    background:red;
}
.vert{
    width:30px;
    height:500px;
    background:yellow;
    position:absolute: left:0;
    top:30px;
}