Sandbox

style.css
setup.css
index.html

/* Setup styles in the other file. */

div:not(:first-child) {
	margin-top: 20px;
}

div:first-child {
	margin-bottom: -10px;
}

body {
	font-family: sans-serif;
	padding: 20px;
}

div {
	background-color: deepskyblue;
	padding: 10px;
	border-top: solid black 4px;
}

<!doctype html>
<html>
	<head>
		<meta charset="utf-8">
		<meta name="viewport" content="width=device-width, initial-scale=1">
		<link href="../assets/reset.css" rel="stylesheet">
		<link href="setup.css" rel="stylesheet">
		<link href="style.css" rel="stylesheet">
	</head>
	<body>
		<section>
			<div>
				<p>This is some text in the first element.</p>
			</div>
			<div>
				<p>And some more in the second element.</p>
			</div>
			<div>
				<p>Then a third one, too.</p>
			</div>
		</section>
	</body>
</html>