@cndragn is on point here - it’s a big world of code out there now - as you start out you may not realize how incredible it is to have such sophisticated and powerful technologies like javascript and chrome, linux and node available for free - this was unthinkable before the rise of open source
the stuff you can use as a complete beginner to solve toy problems is the same stuff used by professionals with decades of experience to solve problems never encountered before - all of us have access to exactly the same sources of information - clearly our needs are different - some need a level of technical precision others may find excessive
HTML, CSS and Javascript are the foundations of web programming - ultimately they are defined by international standards - MDN is a pathway to the standards - compared to the ecmascript spec I assure you MDN docs read like a Robert Ludlum thriller - and ecmascript is quite accessible as standards go
https://www.ecma-international.org/ecma-262/8.0/index.html
So use whatever sources make sense to you - as more things make sense you will naturally gravitate to more authoritative and complete sources of information