JSFiddle - React, Tailwind, and code Playground

HTML

<div id="line">
  <div id="lineleft">left</div>
  <div id="lineright">right</div>
</div>

CSS

#line {
    margin-top: 30px;
    background: blue;
    height: 100px;
}

#lineleft {
    float: left;
    margin-top: -10px;
    background: red;
    height: 30px;
    width: 50%;
}

#lineright {
    float: right;
    background: green;
    height: 30px;
    width: 50%;
}