Resolve "Bug: ACMG dropdown partially hidden on higher zoom"

Description

Changed styling of ACMG dropdown to avoid out-of-bounds.

Also fixes tooltip popup by bringing it up front (was partially hidden in some cases) and adds some other minor styling fixes and cleanup.

Notes to review (code/docs/QA)

Not a perfect solution, but works at all zoom levels. Might consider a different solution for the ACMG selector at some future point (e.g. modal or full-width collapsible section).

Related issues

Closes #2325