code: public B css(String... classes) {
          if (classes != null) {
              List<String> failSafeClasses = new ArrayList<>();
              for (String c : classes) {
                  if (c != null) {
                      if (c.contains(" ")) {
                          failSafeClasses.addAll(asList(c.split(" ")));
                      } else {
                          failSafeClasses.add(c);
                      }
                  }
              }
              for (String failSafeClass : failSafeClasses) {
                  get().classList.add(failSafeClass);
              }
          }
          return that();
      }
docs: Adds the specified CSS classes to the class list of the element.