Handle platform-specific default color for background & foreground properly

[tautcony]

The current configuration has a noticeable issue where using the default cli theme that the background color is always black on *nix platforms, whateve the terminal background color is, e.g:

Currently, the default values for foreground and background colors are based on the Windows configuration. However, on *nix platforms, the situation is different; an explicit value is not set, and the value remains -1 until the application specifies one.

Based on the relevent documentations, I adjusted the default value based on the platform info.
https://learn.microsoft.com/en-us/dotnet/api/system.console.backgroundcolor?view=net-8.0#remarks
https://learn.microsoft.com/en-us/dotnet/api/system.console.foregroundcolor?view=net-8.0#remarks

[tautcony]

However, the current CLI themes might be a bit awkward in another aspect and may need further adjustments, such as white text on a white background.

before:

after:

[calacayir]

However, the current CLI themes might be a bit awkward in another aspect and may need further adjustments, such as white text on a white background.

That's the reason we explicitly set the background color. At the time, I remember I left it like this because being readable is more important. If I remember correctly, it's not possible to detect terminal background color in linux terminals? So we cannot adjust the themes according to the platform?

I will re-examine this.