"vsSwitcher" table class on Wiktionary

Question

I have been looking at implementing Wiktionary's vsSwitcher table class for some time, but cannot find where it is defined. It is used in pages such as the table generator module used for Finnish declensions, as well as multiple other such modules and tables. Where can I find a definition or implementation of it? I am assuming it shows up in a .css file somewhere, but I can't track it down.