Border-images? (three questions)

I've been looking into the border-image css tag and following guides I've found, but it always looks as if the images either don't appear at all or they're squished, like they can't go outside a box that I don't even see in the source code. The only place I've gotten them to show up is on the body itself. Are there any guides or templates for using border images on status.cafe?

Also, I really don't want the background color to get pushed out behind a border that's not covering it. I wanted to use flowers or slime or something, outside the box, not over the background.

I'm having the same issue with the profile picture in that I can't make it any bigger, but I can make it smaller, and I don't know what's blocking it.

Thanks in advance!