Tested on Windows with HCM White.

Reproduced on HCM when the address bar dropdown panel is opened and search mode chiclet is selected.
When the dropdown is dismissed with Escape key, the chiclet won't be visible. If the focus is moved in-page, the chiclet will become visible.

Mozregression returned Bug 1730237 - Split --urlbar-box-focus-bgcolor out from --urlbar-box-bgcolor. r=desktop-theme-reviewers,dao as regressor, Harry could you please take a look? Thank you!

[Tracking Requested - why for this release]:
UI element is invisible in HCM. Low-risk, CSS-only fix is possible.

This patch unifies the HCM colors used in the identity box, the search mode indicator, and the zoom indicator. It uses the HCM convention used in VS Code of using dotted and solid offset outlines to show hover and active states.

Morgan, the attached patch adds a dotted inset outline on an element to denote focus in HCM. The outline becomes solid on :hover:active. I've seen that done in VS Code and it was the best model I could think of here, given the element uses a vibrant background color. What do you think? Is there a better way to show hover/active?

(In reply to Harry Twyford [:harry] from comment #4)

Morgan, the attached patch adds a dotted inset outline on an element to denote focus in HCM. The outline becomes solid on :hover:active. I've seen that done in VS Code and it was the best model I could think of here, given the element uses a vibrant background color. What do you think? Is there a better way to show hover/active?

Thanks for patching this! I'm gonna give it a spin on Windows in a few different HCM themes, and then I'll follow up here with thoughts :)

Added comments on phab :)

https://hg.mozilla.org/mozilla-central/rev/46edc3da8b6c

Comment on attachment 9245928 [details]
Bug 1735643 - Unify Urlbar box HCM behaviour. r?#desktop-theme-reviewers!

Beta/Release Uplift Approval Request

• User impact if declined: The search mode indicator in the Urlbar will be invisible in HCM.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): CSS-only, well-understood.
• String changes made/needed:

Comment on attachment 9245928 [details]
Bug 1735643 - Unify Urlbar box HCM behaviour. r?#desktop-theme-reviewers!

Approved for 94.0b9.

https://hg.mozilla.org/releases/mozilla-beta/rev/1affbae21350

I've managed to reproduce the issue using Fx95.0a1.
The issue is verified fixed using Fx95.0b5 and latest Fx96.0a1 on Windows 10, Ubuntu 20.04 and macOS 11. The one-off ciclet is correctly visible with high contrast mode enabled.