<!DOCTYPE html>
<html>
<head>
<style>
html,
body {
font-size: 16px;
width: 70vw;
height: 40vh;
background-color: yellow;
}
h1 {
background-color: red;
}
</style>
</head>
<body>
<h1>My First Heading</h1>
</body>
</html>