JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

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