_wp_normalize_relative_css_links( string $css, string $stylesheet_url ): string

3157function _wp_normalize_relative_css_links( $css, $stylesheet_url ) {3158	return preg_replace_callback(3159		'#(url\s*\(\s*[\'"]?\s*)([^\'"\)]+)#',3160		static function ( $matches ) use ( $stylesheet_url ) {3161			list( , $prefix, $url ) = $matches;3162 3163			// Short-circuit if the URL does not require normalization.3164			if (3165				str_starts_with( $url, 'http:' ) ||3166				str_starts_with( $url, 'https:' ) ||3167				str_starts_with( $url, '/' ) ||3168				str_starts_with( $url, '#' ) ||3169				str_starts_with( $url, 'data:' )3170			) {3171				return $matches[0];3172			}3173 3174			// Build the absolute URL.3175			$absolute_url = dirname( $stylesheet_url ) . '/' . $url;3176			$absolute_url = str_replace( '/./', '/', $absolute_url );3177 3178			// Convert to URL related to the site root.3179			$url = wp_make_link_relative( $absolute_url );3180 3181			return $prefix . $url;3182		},3183		$css3184	);3185}