>>11820
>>11821
Hello!
Sorry for late reply.
1. you need an image uploaded to somewhere
2. you need the uploaded image's url
3. you have to create a file that contains the rules and name it: custom.css

You already did the first point, you uploaded the image in this post >>11820
You need the url of the image which is:
https://endchan.gg/.media/869459fc7013c39b00fa82882e6dc1f8-imagejpeg.jpg

So now only the rules are missing. I experimented a bit and this could be the most acceptable:

body {
    background-image: url(https://endchan.gg/.media/869459fc7013c39b00fa82882e6dc1f8-imagejpeg.jpg);
    background-repeat: repeat-y;