CSS Box Sizing

<!DOCTYPE html>
<html>
<head>
    <style>
        * { box-sizing: border-box; }
        .kotak-50 {
            width: 50%;
            padding: 20px;
            border: 5px solid #0d2e5c;
            float: left;
            background: #e0f2fe;
            text-align: center;
            font-family: sans-serif;
        }
    </style>
</head>
<body>
    <div class="kotak-50">Kolom Kiri 50%</div>
    <div class="kotak-50">Kolom Kanan 50%</div>
</body>
</html>