JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
    <div class="left"></div>
    <div class="right"></div>
</div>

CSS

.wrapper {
    width: 400px;
    overflow: hidden;
}
.left {
    width: 299px;
    border-right: solid 1px black;
    background: grey;
    float: left;
}

.right {
    width: 100px;
    float: right;
    background: yellow;
}

.left, .right {height: 500px;}