Bug title: The background color of the CommandBar SecondaryCommands pop-up control displayed in WinUI 2(UWP/Xaml islands) and WinUI 3 is inconsistent

### Describe the bug

The background color of the CommandBar SecondaryCommands pop-up control displayed in WinUI 2(UWP/Xaml islands) and WinUI 3 is inconsistent

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CommandBar SecondaryCommands 弹出控件在 WinUI 2(UWP/Xaml islands) 和 WinUI 3 显示的背景色不一致

### Steps to reproduce the bug

See description

### Expected behavior

See description

### Screenshots

See description

### NuGet package version

WinUI 3 - Windows App SDK 1.7.3: 1.7.250606001

### Windows version

Windows 11 (24H2): Build 26100

### Additional context

None

Start by reproducing the CommandBar SecondaryCommands pop-up in WinUI 2 with UWP/XAML Islands and in WinUI 3 using the reported Windows App SDK version. Compare the rendered background colors and relevant control styling; done means the pop-up background is consistent across both environments. No files or tests are named.

Written by the indexing model from the issue text.