Forced Dark navigation item focus ring not visible

[shainanigans]

Describe the bug
In the forced Dark theme (like in Teams), the focus ring on s-navigation--item is not visible.

To Reproduce
Steps to reproduce the behavior:

1. Go to the reference documentation's Theming section and find the Dark theme.
2. Using your keyboard only, navigate to the "Products" link.
3. See that there is no visible focus ring on the link (it's there, just impossible to see).

Expected behavior
Focus ring is visible in the Dark theme. Ring should have 3:1 color contrast ratio with the dark background of the topbar in order to meet color contrast requirements for non-text elements.

Screenshots