JSFiddle - React, Tailwind, and code Playground

HTML

<div id="frame">
    
    <div id="leftCol">
        <div id="1">blah</div>
    </div>
    
    <div id="rightCol">
        <div id="2">blah</div>
        <div id="3">blah</div>
    </div>
    
</div>

CSS

#frame {
    background-color: green;
    width: 500px;
    overflow: auto;
}

#leftCol
{
    width: 245px;
    float: left;
    background-color: red;
}

#rightCol
{ 
    width: 245px;
    float: right;
    background-color: blue;
}