JSFiddle - React, Tailwind, and code Playground

HTML

<div class="left-panel">
        First panel
    </div>
    <div class="right-panel">
        Second panel
</div>

CSS

.left-panel
    {        
        background-color:#ccc;
        width:10%;
        height:100px;            
    }
    .right-panel
    {        
        background-color:Gray;
        width:90%;
        height:100px;
    }