<!DOCTYPE html>
<html>
<head>
<style>
#div1 {
position: absolute;
left: 50px;
width: calc(100% - 100px);
border: 1px solid black;
background-color: yellow;
padding: 5px;
text-align: center;
}
</style>
</head>
<body>
<p>Create a div that stretches across the window, with a 50px gap between both sides of the div and the edges of the window:</p>
<div id="div1">Some text...</div>
</body>
</html>