JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>Тест</title>
<style type="text/css">
#box1 {
        margin:0 auto;
        width:800px;
        height:100px;
        background-color:#F00;
}
#box2 {
        float:left;
        margin-top:10px;
        width:100px;
        background-color:#0F0;
        height:100px;
}
</style>
</head>

<body>
<div id="box1">
    <div id="box2">
    </div>
</div>
</body>
</html>