Administration Screen CSS for changing the styles.

If installing the ‘wp-admin/’ directory will be replaced with ‘./’.

The $_wp_admin_css_colors global manages the Administration Screens CSS
stylesheet that is loaded. The option that is set is ‘admin_color’ and is the
color and key for the array. The value for the color key is an object with
a ‘url’ parameter that has the URL path to the CSS file.

The query from $src parameter will be appended to the URL that is given from
the $_wp_admin_css_colors array value URL.

function wp_style_loader_src( $src, $handle ) {
	global $_wp_admin_css_colors;

	if ( wp_installing() ) {
		return preg_replace( '#^wp-admin/#', './', $src );
	}

	if ( 'colors' === $handle ) {
		$color = get_user_option( 'admin_color' );

		if ( empty( $color ) || ! isset( $_wp_admin_css_colors[ $color ] ) ) {
			$color = 'fresh';
		}

		$color = $_wp_admin_css_colors[ $color ];
		$url   = $color->url;

		if ( ! $url ) {
			return false;
		}

		$parsed = parse_url( $src );
		if ( isset( $parsed['query'] ) && $parsed['query'] ) {
			wp_parse_str( $parsed['query'], $qv );
			$url = add_query_arg( $qv, $url );
		}

		return $url;
	}

	return $src;
}