Improve readability of AccentButton style on High Contrast

[jtippet]

The AccentButton style has a couple problems in High Contrast mode:

• When HighContrastAdjustment is None, the text is completely unreadable.
• When HighContrastAdjustment is Auto, an accented button is indistinguishable from a regular button (unless you have a mouse and hover the pointer over it)

Here are some screenshots. The left column is the current code as-is, and the right column shows the effects of this PR. The screenshot shows a normal button (no special styles) on the left and an accented button (Style="{StaticResource AccentButtonStyle}") on the right. The mouse hovers over the button, then clicks it.

Mode	Current	Proposed
HC Black, Auto
HC Black, None
HC White, Auto
HC White, None
Light theme		[no change]
Dark theme		[no change, although shouldn't the hover background get darker, not lighter?]

Note that this PR undoes #1509. The problem is that that change had made Auto look a little better, at the cost of completely breaking the None mode. I'd argue that the correct fix is for the app that reported the original issue to opt into None mode -- that's the general solution to making your app look great on High Contrast. As long as the app is stuck in Auto mode, a variety of controls will have ugly -- but functional -- automatic backplating. Including accent buttons.

It seems like there is a testing gap here, where the MUX test app doesn't let you try things in None mode. I also raised #2378 to add that as an option.

[ranjeshj]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[zadjii-msft]

Hey all,

We're trying to ingest the MUX v2.4.0-prerelease.200506001 release that included this change in it to the Windows Terminal over in microsoft/terminal#5778. However, I'm fairly certain the changes to the light and dark mode AccentButtonStyle broke the text on those buttons for us. I found that

If you insert

<StaticResource x:Key="AccentButtonForeground" ResourceKey="SystemControlBackgroundChromeWhiteBrush" />

into our App.xaml, that effectively reverts the part of 1785888 that broke this

That change will restore the text to be visible for us, but I don't really know enough about XAML to know what kinds of unintended side effects that might have. Do you guys have any thoughts? Is this something that's a regression up here in MUX itself, or should we try and fix this for ourselves with the App.xaml change?

/cc @DHowett-MSFT

[marcelwgn]

Yes that definitely seems like a regression. Adding the snippet you mentioned should/does not have any side effects since it will override the resource that was falsely changed.

@ranjeshj I will create a PR to revert that change to the default resource if that's fine with you.

[ranjeshj]

Yes. The workaround sounds fine. @chingucoding, lets go ahead and revert it. Thanks!

[zadjii-msft]

Hey just following up - did this ever get reverted?

[marcelwgn]

@zadjii-msft The changes that resulted in the accent buttons to not render correctly have been reverted with #2420 , which was merged into master.

[zadjii-msft]

🤦‍♂️ I even linked to it in the original thread on microsoft/terminal. Thanks for the clarification, I'll make sure to go drink some more coffee now 😝

[marcelwgn]

Haha, happens to all of us 😊