Is there any way to change the colour of The Bell Tree?

I do like the colours of this site, but they're quite bright and I'd like to know if there's any way I can change the background colour of it to solid black or just the nighttime mode. Since I live in the UK, in the nighttime it will still have the daytime colours and it's not very pleasing to look at in my opinion.

I know there may be CSS or HTML involved so if you're going to add that please try to be clear? I'm a coding moron. I have tried the stylish extension and I can't seem to find anything.

Just looking for something easy on the eyes.
Thanks!

There is a button at the very bottom of the left side of the page that says Bell Tree. Click on that drop box and select a few options from that menu. Give that a shot and let me know what you think.

Change the site's timezone to match your own.

Settings -> General Settings -> Date & Time Options

There is no option to set the theme to night. However, as others pointed out, you can adjust your time zone in settings or try using the TBT Undercover theme option which may be preferable for you.