/* Setup styles are in the other file. */

/* This applies to both. */
div:not(:first-child) { margin-top: 40px; }

/* But this negates some of it. */
div:first-child { margin-bottom: -30px; }
body {
	font-family: sans-serif;
	padding: 20px;
}

div {
	background-color: deepskyblue;
	border-top: solid black 4px;
	padding: 10px;
}
<!DOCTYPE html>
<html>
	<head>
		<title>Margin negative</title>
		<link href="/assets/styles/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>