WordPress at a glance
function is not described

wpmu_activate_stylesheet() WP 3.0.0

Loads styles specific to this page.

No Hooks.

Return

Nothing (null).

Usage

wpmu_activate_stylesheet();

Code of wpmu activate stylesheet: wp-activate.php VER 5.1.1

<?php
function wpmu_activate_stylesheet() {
	?>
	<style type="text/css">
		form { margin-top: 2em; }
		#submit, #key { width: 90%; font-size: 24px; }
		#language { margin-top: .5em; }
		.error { background: #f66; }
		span.h3 { padding: 0 8px; font-size: 1.3em; font-weight: 600; }
	</style>
	<?php
}