JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<link rel="stylesheet" type="text/css" href="KKF_00005.css">
<title>KKF 5: Border coping</title>
</head>
<body>
    <div class="links_aussen">
        Rechts
    </div>
    <div class="mitte_aussen">
        Mitte
    </div>
    <div class="rechts_aussen">
        Links
    </div>
</body>
</html>

CSS

@CHARSET "ISO-8859-1";

* {
    height: 100%;
    margin: 0;
    padding: 0;
}

html,body {
    background-color: grey;
    width: 100%;
}

.links_aussen, .mitte_aussen, .rechts_aussen {
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    -ms-box-sizing: border-box;
    -o-box-sizing: border-box;
    box-sizing: border-box;
    border: 1px solid black;
}

.links_aussen {
    float: left;
    background-color: green;
    width: 33%;
    height: 100%;
}

.mitte_aussen {
    float: left;
    background-color: yellow;
    height: 100%;
    width: 34%;
}

.rechts_aussen {
    float: left;
    background-color: red;
    height: 100%;
    width: 33%;
}