OK. No shame, your HS math is like college math in the US ;-) Best math book I have ever bought was the English translation of the first edition VNR Concise Encyclopedia of Mathematics (E Germany). by Gellert et al Editors. The upper level chapters cover Galois theory!

I also liked the first edition CRC Concise Encyclopedia of Mathematics (USA) by Weisstein.

Anyway, do you have a favorite math channel on YouTube?