Traditionally, I remember the rule that presentation should be managed by css, while behavior should be managed by javascript. But does the fact that some things can be reasonably done either way change - for example - a site's or app's maintainability? How about it performance? Is a CSS implementation rendered faster than javascript? I struggle with this at times, especially in some cases where - admittedly older - frameworks allowed for some overlap. Ah, well, much like lots of the web, i'll just work to get stuff done.