Improve menu item selection border for themes (#319306)

* theme: add selection border for menu items in light and dark themes

Co-authored-by: Copilot <copilot@github.com>

* theme: improve specificity for high contrast menu selection border

Co-authored-by: Copilot <copilot@github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

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Co-authored-by: mrleemurray <mrleemurray@users.noreply.github.com>
Co-authored-by: Copilot <copilot@github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>