What is the benefit of separating code by file type? If your reasoning is to reduce coupling, I think this is false simplification - again, in complex applications with lots of interaction, there is no escaping the coupling of DOM nodes, JS logic, and styles. Any feature changes change is going to need to modify all three. Maybe for a mostly read-only site de-coupling these things makes sense, and you can achieve your goals with something like Bootstrap, where you compose a bunch of reusable CSS classes. But for the majority of work I’ve done over the last 8 years, that decoupling model doesn’t work. It’s an even harder nest of snakes when you multiply 3 screen sizes x 2 input methods x N pages where CSS could be used - again for something simple, it’s fine to just collapse columns on mobile (the typical CSS column-css-6 style) but frequently you want this stuff to be much more responsive to user device and input than decoupled styles allows.