Improve docs styling and structure

[Blargian]

Placeholder issue for improvements we can make to docs styling and page structure.

Ideas from discussion with Cristina:

• Use titles more effectively
• Use indentation (see BigQuery docs for very effective use of indentation)
• Add white space between sections, even paragraphs
• Style certain elements so that they pop up
• Define a max width of…. 880, test it, see how it goes.
• Increase the line height of regular text to 175%
• Experiment with regular text size 16px (we use 14px)
• get rid of the line rule between sections (makes pages feel like 'boxed' information rather than a narrative)

Examples of documentation with good design that encompass some of the above changes:

https://supabase.com/docs/guides/database/overview
https://vercel.com/docs/observability
https://linear.app/docs/start-guide
https://docs.stripe.com/
https://vuejs.org/guide/introduction.html