Fix the Button border and color with FlatStyle = Flat: FlatAppearance properties

[LeafShi1]

Fixes #13897

Proposed changes

• Add MouseDownBackColor and MouseOverBackColor for Flat button in DarkMode
• Add borderSize and borderColor drawing logic to Flat button

Customer Impact

• The FlatAppearance property can be set normally in DarkMode

Regression?

• No

Risk

• Minimal

Screenshots

Before

FlatAppearance settings are ignored

button3.BackColor = Color.Transparent;
button3.FlatAppearance.BorderSize = 5;
button3.FlatAppearance.BorderColor = Color.Yellow;
button3.FlatAppearance.MouseOverBackColor = Color.Purple;
button3.FlatAppearance.MouseDownBackColor = Color.Red;

beforeChange.mp4

After

All of the FlatAppearance properties work well

AfterChanges.mp4

Test methodology

• Manually

Test environment(s)

• .net 10.0.0-rc.1.25467.108

Microsoft Reviewers: Open in CodeFlow

[codecov]

Codecov Report

❌ Patch coverage is 0% with 31 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.14583%. Comparing base (5a9fb88) to head (e58f2ab).

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13898         +/-   ##
===================================================
- Coverage   77.15021%   77.14583%   -0.00438%     
===================================================
  Files           3274        3274                 
  Lines         645043      645064         +21     
  Branches       47701       47705          +4     
===================================================
- Hits          497652      497640         -12     
- Misses        143717      143742         +25     
- Partials        3674        3682          +8     

Flag	Coverage Δ
Debug	77.14583% <0.00000%> (-0.00438%)	⬇️
integration	18.98383% <0.00000%> (-0.01568%)	⬇️
production	52.00495% <0.00000%> (-0.00796%)	⬇️
test	97.41286% <ø> (ø)
unit	49.42222% <0.00000%> (+0.00056%)	⬆️

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[Copilot]

Pull Request Overview

This PR fixes button border and color issues for buttons with FlatStyle = Flat by implementing proper support for FlatAppearance properties in dark mode. The changes ensure that MouseDownBackColor, MouseOverBackColor, BorderSize, and BorderColor properties are respected when rendering flat buttons in dark mode.

Key changes:

• Extended button renderer interfaces and implementations to support border size and color parameters
• Added logic to respect FlatAppearance MouseDownBackColor and MouseOverBackColor properties
• Updated all dark mode button renderers to handle the new border parameters

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
ButtonDarkModeAdapter.cs	Added logic to use FlatAppearance MouseDownBackColor and MouseOverBackColor, and pass BorderSize/BorderColor to renderers
IButtonRenderer.cs	Extended interface to include borderSize and borderColor parameters in method signatures
ButtonDarkModeRendererBase.cs	Updated base class to support new border parameters and added virtual DrawButtonBorder method
FlatButtonDarkModeRenderer.cs	Implemented proper border handling using FlatAppearance properties and simplified border drawing
SystemButtonDarkModeRenderer.cs	Updated method signature to match interface changes
PopupButtonDarkModeRenderer.cs	Updated method signature to match interface changes