function transformCss(css, transformClassName, filter) {
	const ast = compile(css);
	currentTransformClassName = transformClassName;
	currentFilter = filter;
	return serialize(ast, middleware([prefixClasses, filterRules, stringify]));
}
Transform a StyleSheet, applying a suffix to classNames.
@NOTE Currently not used. May be used in the future by `wmr/styles-plugin`.

@param {string} css StyleSheet text
@param {(className: string, additionalClasses?: string, specifier?: string) => string} [transformClassName] A function to remap classNames to namespaced version
@param {(element: object) => boolean | empty} [filter] Optionally filter returned rules
@returns {string}