They recently had a code update: https://lichess.org/blog/XMvcJSwAADkA0hPE/lichess-v2-is-here, I find it amazing that the website works equally well regardless of the device.
I also love and admire their anti advertisement attitude:
Indispensible practice material:
Basics: https://lichess.org/learn#/
Tactics: https://lichess.org/practice