Description
Visual bug, the description is here:
https://github.com/elastic/UX/issues/120#issuecomment-2389313420

Serverless project type:
Observability (but it's probably in other solutions as well)

Browser:
Chrome 128.0

Describe the bug:
Border top of navigation side-bar is inconsistent between light and dark theme.

Screenshots:
Light theme

Dark Theme

Steps to reproduce:

1. Just switch between light and dark theme, and vice-versa, to notice it

Expected behavior:
I would expect that border, on dark theme, to be identical (lighter) to the right border of the side-bar, as it is on light theme

Additional context
It might be a bottom-border from the top bar instead of a border-top from navigation side-bar, not entirely sure