dropdownClassName class does not appear in DOM

[givethemheller]

dropdownClassName does not appear to be working - creating a "test-class" does not appear in the DOM when added.

Repro Steps

1. clone and build the repo
2. Open basic.js and add the dropdownClassName property to the "single select" demo with the class name "test-class".
3. Search the DOM for "test-class" - test-class does not appear in the DOM