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 depend…
Trouble with CSS is still this: https://media.giphy.com/media/yYSSBtDgbbRzq/giphy.gif (Peter Griffin trying CSS) And centering a div can still be very hard depending on the circumstances.
Are the circumstances that you are banned from using flex or grid?