Opacity

index.html

					<!doctype html>
<html>
	<head>
		<title>Opacity</title>
		<link href="/assets/reset.css" rel="stylesheet">
		<link href="setup.css" rel="stylesheet">
		<link href="style.css" rel="stylesheet">
	</head>
	<body>
		<section>
			<p>This is some text in the first element.</p>
		</section>
		<section>
			<p>And some more in the second element.</p>
		</section>
		<section>
			<p>Then a third one, too.</p>
		</section>
	</body>
</html>

setup.css

					/* Same as before. */
:root { --spacing: 1rem; }

body {
	font-family: sans-serif;
	padding: var(--spacing);
}

section {
	background-color: var(--background, deepskyblue);
	border-block-start: solid black calc(var(--spacing) / 5);
	padding: var(--spacing);

	&:not(:first-child) { margin-block-start: var(--spacing); }
}

style.css

					/* “See through.” */
section:nth-child(2) { opacity: 0%; }

/* “Semi-transparent.” */
section:nth-child(3) { opacity: 50%; }