JSFiddle - React, Tailwind, and code Playground

HTML

<div id=leftFrame>
    <div id=tabs>
        <div>first</div>
        <div>second</div>        
    </div>
</div>

CSS

* { box-sizing:border-box; }
#leftFrame {
    background-color:green;
    position:absolute;
    left:0;
    right:60%;
    top:0;
    bottom:0;
}
#leftFrame #tabs {
    background-color:red;
	position:absolute;
	top:0;
	left:0;
	right:0;
	height:25%;
}
#leftFrame #tabs div {
    border:2px solid black;
	position:static;
	float:left;
	width:50%;
	height:100%;
	text-align:center;
	display: inline-flex;
	align-items: center;
}