[Style] Update modals to increase readability on High-Contrast Theme

[Aliandi]

Fixes issue #1312

Changes made

• Update .dialog color and bg-color of the high-contrast theme to match the theme's palette.

[tonyanziano]

Thanks for the PR!

Left some comments for some minor improvements. Otherwise, great work!

[tonyanziano]

Try a similar approach to what I wrote below for the --error-text variable. It would be great to have a --dialog-color variable or something similar that each theme could control without having to use `!important.

[Aliandi]

We've been trying this approach with no luck yet, but we'll keep looking into it!

[tonyanziano]

I've added a commit that's working on my end. Please try it locally and see if that works! 😃

[tonyanziano]

Also, it would be great if you could add an entry to the change log.

Under Unreleased and above v4.3.3 you can add a new section for Fixed and put your entry under that.

[coveralls]

Pull Request Test Coverage Report for Build 2255

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 55.177%

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Totals
Change from base Build 2242:	0.0%
Covered Lines:	4883
Relevant Lines:	8319

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💛 - Coveralls

[cleemullins]

Also, it would be great if you could add an entry to the change log.

Under Unreleased and above v4.3.3 you can add a new section for Fixed and put your entry under that.

Over in the BotBuilder SDK, we have a script that pulls the PR comments for all PRs in a given date range. We use that to create the release notes & changelog at the end of each cycle. You guys are more than welcome to share that!

[justinwilaby]

This PR is at odds with the original requirements for modals in the Emulator. Before this is merged, it should go through a design review and get sign off:

[justinwilaby]

Hold until design review is performed.

[cleemullins]

@justinwilaby What's the process for a design review?

[cwhitten]

@cleemullins it's as simple as assigning a Bot Framework Designer! I'll go ahead and do this. @mewa1024 can you revisit the direction to override the theme variables in all modals? I'm wondering if this break accessibility requirements in High Contrast mode. Justin tells me the VSCode does something similar. This is odd to me.

Design review completed

[mewa1024]

Yes, the black background for High Contrast mode is fine.