<!DOCTYPE html>
<html>
<head>
<style>
div {
font-size: 30px;
border: 1px solid black;
}
span {
font-size: 1ex;
}
</style>
</head>
<body>
<div>The font-size of the div element is set to 20px. <span>The span element inside the div element has a font-size of 1ex</span>.</div>
</body>
</html>