fix links to focus on linked header

[tholok97]

Navigating and linking to headers doesn't focus on the header. This has annoyed me a bit. Here's a fix:

Action	master	this PR
Clicking a heading on the right-hand menu
Opening link like https://docs.waterlinked.com/sonar-3d/sonar-3d-15-api/#imubatch

Please help me functionally review by uv run mkdocs serve, opening localhost:8000 and clicking around. Help me verify styling works as expected.