Does the CSS customization feature depend on the selected form layout?

Does this feature depend on the form? I use a card form and the form designer only shows "Themes" and "Individual" where I can set some (not all colors) but no CSS.

Unfortunately, Car Forms do not have the option to be customized with CSS code. Only the classic form layouts have it, so you might want to switch your form to the classic layout:

Let us know if you have more questions.