Along this theme of knowledge, there is the lost art of tuning your page and content sizes such that they fit in as few packets as possible to speed up transmission. The front page of Google for example famously fitted in a single packet (I don't know if that's still the case). There is a brilliant book that used to be a bit of a bible in the world of web sysadmin from the Yahoo Exceptional Performance Team which is less relevant these days but interesting to understand the era.

https://www.oreilly.com/library/view/high-performance-web/97...

I'll add some perf suggestions:

High Performance Websites and Even Faster Websites http://shop.oreilly.com/product/9780596529307.do http://shop.oreilly.com/product/9780596522315.do

These two on website performance are good, though they're a bit dated (pre http2 etc).

High Performance Browser Networking http://shop.oreilly.com/product/0636920028048.do

I never fully read this one but it's really good, probably required reading if you're serious about webdev

CSS: BEM/OOCSS/SMACSS methodologies, they make you think critically about the structure of you styles. Harry Roberts does good writeups on maintainable css.

I second Don't Make Me Think and I also liked Eloquent Javascript (that zoo has a bunch of new exotic animals since, so I don't know if it's the best bet. It's a fun book though)