(not sure if you still need help with this)
if you’re looking to add a background for those, first you’ll need to disable WYSIWYG where you’re going to be using code at
you can permanently disable it in your settings under “Display Settings” here: https://toyhou.se/~account/display
-> under WYSIWYG Settings, uncheck “Profile Text”, click the Update WYSIWYG Settings button, then in the Editor Settings above it, checkmark the “Enable Code Editor” and click the Update Editor Settings button
from there, you can use background html like this one to add it into your user/character profiles and folders, do be sure you are using a direct image address (ones ending in .jpg / .png / .gif) for your images
I do want to note: if you‘re trying to get the same image as a background for every page (including design/art tabs, unsorted folder, etc.), that will require premium as that is a CSS feature, however if you’re just looking to put backgrounds on your profile / characters / individual folders, the steps above will work just fine