Hi Roslyn,
This is Wil, one of the independent advisor, an expert with Windows 10 and a fellow Windows 10 user like you. I understand your concern about the black background on GMAIL.
If you are using the gmail.com website and have a black background, it means that the theme is set to dark mode.
To activate dark mode for Gmail on the desktop, go to Gmail.com and click the 'Settings' icon (shaped like a gear) at the top right underneath your profile picture. Select 'Themes', scroll past the various picture themes and click the default thumbnail. You may hover your mouse on it to show the name of the theme.
I hope my suggestions help you. If you need further assistance please do reply back and I will respond as quickly as possible. Have a nice day.
Thanks,
Wilfred P.
Independent Advisor