Answer 1

W3Schools and MDN are very good in all regardas. Sololearn is okay but if you really wanna learn something go with the first two.

Answer 2

"And please no biased answers."
That one was kinda tough. Given the discussion topic concerns learning sources comparison, it's hard to exclude personal preferences ¦ )
By the guidelines this might be considered as an opinionated or open-ended topic.
https://www.sololearn.com/Discuss/1316935/?ref=app

Answer 3

You shouldnt make anything your primary source of coding knowledge.
Use everything the same and compare the knowledge you get.

Answer 4

Learn w3school HTML and CSS
Others programming language learning Sololearn bcz it's good and easy to learn