Few table updates:
- Fixes the inverse table's border color. Adds a new variable that lightens the inverse table's background color a bit instead of using
$body-bg. - Fixes the responsive table behavior. Instead of using a parent class again, this scopes (as the comment above it indicates) the styles to under 768px.
Fixes part of #21585 (closed) Fixes #21577 (closed) (/cc @pmsaue0 as credit for the fix) Closes #21677, closes #21678, and closes #21676 as they're no longer needed.