JSFiddle - React, Tailwind, and code Playground

by Amandeep Singh

HTML

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

CSS

.header {
    background-color: green;
    display: inline-block;              /*added*/
    width: 200px;
}
.left {
    background-color: red;
    float: left;           /*added*/
    height: 50px;
    width: 50px;
}
.float_R {
    background-color: blue;
    float: right;
    height: 50px;
    width: 50px;
}