WordPress at a glance
filter is not described

wp_admin_css filter-hook . WP 2.3.0

Filters the stylesheet link to the specified CSS file.

If the site is set to display right-to-left, the RTL stylesheet link will be used instead.

Usage

add_filter( 'wp_admin_css', 'filter_function_name_9868', 10, 2 );
function filter_function_name_9868( $stylesheet_link, $file ){
	// filter...

	return $stylesheet_link;
}
$stylesheet_link(string)
HTML link element for the stylesheet.
$file(string)
Style handle name or filename (without ".css" extension) relative to wp-admin/.
Default: 'wp-admin'

Where the hook is called

wp_admin_css()
wp-includes/general-template.php 4037
echo apply_filters( 'wp_admin_css', "<link rel='stylesheet' href='" . esc_url( wp_admin_css_uri( $file ) ) . "' type='text/css' />\n", $file );
wp-includes/general-template.php 4041
echo apply_filters( 'wp_admin_css', "<link rel='stylesheet' href='" . esc_url( wp_admin_css_uri( "$file-rtl" ) ) . "' type='text/css' />\n", "$file-rtl" );

Where the hook is used (in WP core)

Does not used.