I also don't need to hunt down CSS files because I rarely ever got more than 5 css files in projects I authored myself usually more like three: style.css for general stuff, fonts.css for fonts and multiple foo.css for page/section-specific stuff that isn't needed elsewhere thus only one of those is ever loaded.
For most "theming"-like stuff I make extensive use of css variables I want all my things to look like the button? Well just add the same styling with the variables in place.
As for the divide between HTML and CSS: to me HTML is 99% semantic. That means I describe the information as it should be described and the rest is done in CSS. Nowadays I rarely ever feel the need to create useless divs or go back and edit the HTML to fix styling issues thanks to grid layouts.
It wasn't always that way, but thst was to a degree the point of the linked article as well.
