fixed background image height inconsistent

I want my background image to show as it does in Firefox for all browsers (centered & filling the window from top to bottom). I don’t mind that the light blue solid background color shows on the left and right, but the background image should cover the screen from top to bottom. I’m learning as I go, so any help would be wonderful. Thank you!!

https://naminori760.com/

This is my CSS:

[CSS moderated as per the Forum Rules. Please just post a link to your site.]