“Ctrl+/”
“F11/ESC”
<!DOCTYPE html>
<html>
<head>
<style>
p.ex1 {margin:2cm 4cm 3cm 4cm}
</style>
</head>
<body>
<p>A paragraph with no specified margins.</p>
<p class="ex1">A paragraph with specified margins.</p>
</body>
</html>