If you use Panels Pages for the bulk of you site building, you may have noticed that there are frequent limitations on some of the more random pages.
An example is the comment confirmation delete form. I don’t need much on this form, the stock info is fine, but I want to add my logo at least. I don’t use the logo function that Drupal provides standard, I implement it with my own CSS.
On the form, I use the background element on the #node-confirmation-form ID to add the logo via the CSS shown in the SS. But since that places the background right underneath the form text, I have to tweak it a bit to move things around so that they look OK. I ended up using a combination of height, top, padding and relative positioning. I really just had to experiment until I got it right.
This is not the best approach, but it is a good quick and dirty way to customize a form strictly through CSS when Page Manager doesn’t offer to intercept it for you.