Try it Editor

<!DOCTYPE html>
<html>
<head>
<style>
div {
  height: 300px;
  width: 100%;
  background-color: palegreen;
}
</style>
</head>
<body>
 
<h2>Set the height and width of an element</h2>
 
<p>This div element has a height of 300px and a width of 100%:</p>
 
<div></div>
 
</body>
</html>