[Dark Mode] Improve contrast of soft context menu highlight
[Dark Mode] Improve contrast of soft context menu highlight

The default --color-primary is a bit light to use for this - will ping
the UX folks to ask what they'd like long term, but for now I've
changed it back to the color it was before softContextMenu.css was
migrated as part of the dark mode work.

Fixed: 1222956
Change-Id: Ie25f5c2889ef7dd8944d59b304d11b98adfaed24
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2988305
Auto-Submit: Jack Franklin <993fcadce4d04090da2fefd557a0995e7966c8d5@chromium.org>
Commit-Queue: Paul Lewis <8915f5d5c39a08c5a3e8a8d7314756e4580816f9@chromium.org>
Reviewed-by: Paul Lewis <8915f5d5c39a08c5a3e8a8d7314756e4580816f9@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend