How to learn web design if backround is on mathematics and data analysis?
Just about everything you need can be found in one or another book. O'Reilly has a large selection of reputable work. (No affiliation) But a topical search online or at Amazon will get you what you need. 

If you prefer video, a search at YouTube, say, will turn up lots of possibilities. 

Prefer recent books and videos, however. Straight html is seldom used for serious work these days.