Legibility enhancement for headings

[hermeneuticlens]

I really love AFFiNE so far, but one thing that has been bothering me is the headings. They are unnecessarily large, and various levels of headings (h1-h3 in particular) are very difficult to be distinguished, especially in reality where they appear next to each other in a long text. Notion does a better job, and MediaWiki is still the best (for Headings 1-3, which in MediaWiki are called Levels 2-4 ... ). When I was using Obsidian in the past, I implemented an indentation scheme using CSS. I like my solution a lot, despite few others seemingly doing the same.

I am happy to submit a PR but thought it is probably prudent to ask for community's opinions and preferences. Thanks!