How to change toolbar color and Force dark mode only ?

[chzappsinc]

Can you show an example of how to change the title bar colour, I have given it in the app manifest but it only reflected in the splash screen

And how to force Dark mode only
I have tried Theme=Dark in XAML but it's not reflecting

Support from stackoverflow and react-native-windows solutions are different,

I am new to Windows

Please response @chrisglein