> When the number of nested selectors becomes too great it can become very difficult to reason about.
This is a sign you need to decompose whatever design you are working on into smaller components. If you’re trying to write styles for a whole page at once, you’ll see this problem, but if you are working on small components, it’s very rare.
Not precisely a module system, but you at-least get scoping if you use web-components where you can restrict CSS to the scope of the web component. (There are CSS module systems, but they are not covered by a standard and use JS libs)
The problem is that web-components need JS enabled, which really, really sucks. Why should a component that can perfectly render itself using plain HTML and CSS need to have associated JS declaring: "Hey! I am a web-component!". Declarative web components would have made adoption of web-components super-high , but alas, corporate interests are against this feature.
This is a sign you need to decompose whatever design you are working on into smaller components. If you’re trying to write styles for a whole page at once, you’ll see this problem, but if you are working on small components, it’s very rare.