Changing Background Color Of A Template

[Dianamoon]

There have been no discussions about this since 2016 so I'll bring it up again.

I found an older template that works for me but the background is black. I'd rather soften it. Is there a way to do this? 

I have tried the colored circles in the bar on the left in the "Theme" tab but that doesn't work.

I am willing to learn some HTML for this.

[NJRFTF]

@Dianamoon 

Url of your website?

[Dianamoon]

Update: problem solved by customer service.

The template can't be changed.