++ rainbow border (for image rooms without text)

btw, this was surprisingly hard to make
as rpr haaaates linear gradient
and border-images
and even background images...
I hate writing ugly code, but I just had to ><

code for 400x300 images. https://pastebin.com/wGzgf8D2
you can tweak if you please and know how to.
don't remove credits, don't claim as your own.