JSFiddle - React, Tailwind, and code Playground

HTML

<div class="header">
    <div class="left"></div>
    <div class="float_R"></div>
</div>

CSS

.header {width: 200px; background-color: green;overflow:hidden;}
.left {width:50px; height: 50px; background-color: red;}
.float_R {width:50px; height: 50px; background-color: blue; float:right;}