Well Black is the new Red... What can I say.. I think it clears a lot of clutter and you feel focused on the right things.
Right to the meat.
nnn
For Switching Dark Mode in Windows 10. Just search for "Dark Theme" in Cortana and you should get the below option
Just change the present setting to Dark and you should be golden.
Next Outlook . Goto File->Options->General
Here you will find a setting Personalize your copy of Microsoft Office
Next SSMS ->
First open a notepad with "Run as Admin". Then open the file ssms.pkgundef and find the line "Remove Dark Theme".
You should find the file in C:\Program Files (x86)\Microsoft SQL Server Management Studio 18\Common7\IDE. I have version 18 hence this path you can do a search for the file in "program files (x86) folder". Once you find the line just comment the line with "//" without the quotes as shown in the image below.
Once done save the file and then open the SSMS. Goto
Tools->Options->Environment->General->Colour Theme-> Dark