height-width.css

/* <!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Height-width</title>
    <link rel="stylesheet" href="style.css">
<body>

    <div class="container">
        <div class="box">
            <h2>This is #1</h2>
        </div>
        <div class="box">
            <h2>This is #2</h2>
        </div>
    </div>
    
</body>
</html> */

/* style.css */

* {
    box-sizing: border-box;
}
.container{
    background-color: hsl(0, 0%, 24%);
    height: 100vh;
}
.box{
    background-color: hsl(0, 0%, 100%);
    border: 2px solid;
    padding: 25px;
    height: auto;
    width: 50%;
    float: left;
    text-align: center;
}