Adding the option for custome themes

Is your feature request related to a problem? Please describe

Hi there, I really like the look and how responsive everything feels, but I would love if there was an option to add my custome themes with my own background, primery, secondary and accent, and I want to be able to change between my styles with ease like the switch between the native dark and light themes.

I would also appreciate if I could have accses to my color palette from the XAML so I could add my own styles and templates that can blend with the library elements.

Describe the solution you'd like

for the themes I would love to have a class like:

class Theme{
public Color Primery{get;set;}
public Color Backgournd{get;set;}
public Color Secondary{get; set;}
public Color Accent {get; set;}
public Theme(Color primery, Color background, Color secondary, Color accent){
Primery = primery;
Secoundry = secondary;
Backgroud = background;
Accent = accent;
}

and then be able to do ApplicationThemeManager.Apply(Theme);.

and for the palette accsess in the XAML I just want to be able to do {ui:Background} or {ui:Primery}

Describe alternatives you've considered

No response

Additional context

No response

Start by reviewing the existing theme-management entry point referenced as ApplicationThemeManager and the current XAML resource or palette usage. Done would mean supporting user-defined themes, switching between them, and exposing palette values for custom XAML styles and templates.