I don't think there's a reason why he chose to not go with JS, but to show that it's possible with only CSS. IMO I like using less JS because it slows down th

I don't think there's a reason why he chose to not go with JS, but to show that it's possible with only CSS. IMO I like using less JS because it slows down the Mobile web experience. JS is super powerful and you get to do cool things with it but you always have to keep an eye out for performance.