What's your internal technical documentation like?

I am really interested in how engineering teams do their internal technical documentation especially frontend teams. Is there a particular structure or is it just READMEs?

The main focus here is seamless on-boarding of new team member(s).

E.g for backend team, our doc structure is typically:

• Overview (about the project, structure of the team etc)
• Getting Started (how to setup, environments quirks etc)
• Database (Info about the collections/tables, decisions behind designs, structure etc)
• Cloud Functions/APIs (Self explanatory)
• Best Practices (Testing, style guide)

So, what's it like at your workplace? Please share.

Thanks!