index.html

<!doctype html>
<html lang="en">
<head>
<title>BuckysRoom</title>
<link rel="stylesheet" href="index.css">
</head>
<body>
<div>This is normal text</div>
<div class="one">This is 1em</div>
<div class="two">This is 1.5em</div>
<div class="three">This is 2em</div>
</body>
</html>


index.css

body{
font-size: 100%;
}
.one{
font-size: 1em;
}
.two{
font-size: 1.5em;
}
.three{
font-size: 2em;
}