Fix 13627 DemoConsole app: The open button cannot be seen in TreeView Tasks dialog in Dark Mode

[Epica3055]

Fix #13627

Root Cause

We did custom painting in protected override void OnPaint(PaintEventArgs e) and this method only get invoked when OwnerDraw is true. But now the parent class OwnerDraw 's logic is changed , that makes OwnerDraw false.

Proposed changes

• We need to set OwnerDraw true to be able to draw the button ourselves. So we set FlatStyle to Popup to break parent class's OwnerDraw logic.

Screenshots

Before

After

Test methodology

• manual test

Microsoft Reviewers: Open in CodeFlow

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 76.60343%. Comparing base (08485db) to head (4f9ddac). Report is 8 commits behind head on main.

Additional details and impacted files

@@                 Coverage Diff                 @@
##                main      #13631         +/-   ##
===================================================
- Coverage   76.60828%   76.60343%   -0.00485%     
===================================================
  Files           3253        3253                 
  Lines         640996      641000          +4     
  Branches       47439       47439                 
===================================================
- Hits          491056      491028         -28     
- Misses        146290      146322         +32     
  Partials        3650        3650                 

Flag	Coverage Δ
Debug	76.60343% <0.00000%> (-0.00485%)	:arrow_down:
integration	18.99043% <0.00000%> (-0.00341%)	:arrow_down:
production	51.05856% <0.00000%> (-0.01045%)	:arrow_down:
test	97.41175% <ø> (ø)
unit	48.43719% <0.00000%> (-0.00971%)	:arrow_down:

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[LeafShi1]

Please add Root Cause in the description