High Performance Websites and Even Faster Websites
These two on website performance are good, though they're a bit dated (pre http2 etc).
High Performance Browser Networking
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.