Learn how to add, remove and test for CSS classes using the classList API. It's more powerful than using
className and doesn't require any dependencies.
I guess you can have only one button named "toggle filter" (or even a dynamic button text which changes depending on whether the class is applied or not) and then just use classList.toggle('filtername') without a second attribute, which is essentially how .toggle works. (just saying it because it's not clear from the video)