You weren’t kidding when you said it’s “very hidden”. It didn’t even occur to me that the greyed out “Community…” text was a search box. No borders, and the text formatting does not attract attention at all.
I think even a slightly contrasting background would / magnifying glass glyph would better indicate you can search there.
Oh yeah. This is quite fun, though once you hit level 4/5 some problems require fairly advanced algorithms / mathematics. One of the problems I gave up on solving on my own required knowledge of Polyas enumeration theorem to solve. Fortunately or unfortunately you can find some answers online, otherwise I would’ve never even known such a theorem existed.
For the tougher problems, expect a lot of graph theory / combinatorics, which I guess is the nature of Googles challenges as a search engine.