You don't need much expertise in CSS to build common web UI patterns. It's been around a long time, and tropes like "it's hard to center a div" aren't really true anymore.

It's absolutely possible to build JavaScript apps in a single page with no external dependencies. All you need is a single .html file and a simple development server (I use python http.server).

Writing in typescript is a easy as a single dev dependency to compile the code. There's no multithreading but first class async support.

Additionally, JS / TS are very flexible. You can implement almost any programming paradigm you want to learn. I love doing FP in typescript personally.