JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div class="left"></div>
    <div class="right"></div>
</div>

CSS

#container {
    width: 100%;
    position: relative;
}

#container div { 
    height: 100px; 
}

.left {
    background: green;
    position: absolute;
    top: 0;
    width:2px;
    
    left: 0;
    right: 20px;
}

.right {
    position: absolute;
    background: red;
    width: 250px;
    top: 0;
    right: 0;
}