I accidently reverted the file on the edit html and css and now my website template is messed up and now it's like this; how do I restore the previous version?

I'm afraid, this would have completely removed your custom templates. The only way to restore it would be to restore you community to a previous backup but you would lose any content/data/etc... made after the backup was taken. As you're on Cloud, we can do this, please let us know if you would like to continue and we can move this to a ticket to proceed.

Where can I find the previous backup?

This would need to be something we do for you. Do you want to proceed? If so, I can transfer this to a ticket to answer any questions and get this going.

Yes, I want to proceed please. Can you please restore the backup from april 10, because I think the accident of css revert change happens on April 11th morning. Please get back to me as soon as possible please, thanks!

I have transferred this to a ticket for you, and someone will be in contact as soon as possible

thanks!