You can go to preferences, (under rules by the logout button), and then click profile. In the Text/HTML box you can write your own code, but I believe it must be html. I'm no good at coding but if you want to place a background image, you can use this code:
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For pet pages, go to your profile and under the pet will be an edit pet page button. Just click that and you can add in code to a pet page. idk how that works xD You can always ask someone else to code it for you lol