JSFiddle - React, Tailwind, and code Playground

HTML

<div id=left_thingy>
</div>
<div id=container>
    <div class=auto_width>
    </div>
    <div class=auto_width>
    </div>
    <div id=mid_col>
    </div>
</div>

CSS

div { height: 200px; }
#left_thingy { position: absolute; width: 199px; background: orange }
#container { padding-left: 200px; position: relative;}
.auto_width { width: 50%; background: red; outline: 1px solid white; float: left}
#mid_col { width: 100px; background: rgba(0,255,0,.5); position: absolute; left: 50%; margin-left: 50px; }