I agree somewhat for web pages, but this looks like a maintenance disaster for a web app of any significant size. I will probably turn down any offer to work on

I agree somewhat for web pages, but this looks like a maintenance disaster for a web app of any significant size. I will probably turn down any offer to work on a team with a large project that uses this approach, unless fixing it would be part of my job. For web apps, I contend that modularity ought to be the goal for HTML, JS, and CSS. In the project I'm working on now, each widget/component has its HTML, JS, and CSS together in a single folder. When a widget/component is first loaded, its CSS is added to the DOM. Each component has a unique parent class name, and all its markup and styles are nested under it. Having cross-cutting styles that are re-used throughout the app sounds decidedly un-modular. Why not re-use components/widgets instead?