One cool thing aboutidattributes is that, like classes, you can style them using CSS.
However, anidis not reusable and should only be applied to one element. Anidalso has a higher specificity (importance) than a class so if both are applied to the same element and have conflicting styles, the styles of theidwill be applied.
Here's an example of how you can take your element with theidattribute ofcat-photo-elementand give it the background color of green. In yourstyleelement:
Note that inside yourstyleelement, you always reference classes by putting a.in front of their names. You always reference ids by putting a#in front of their names.
Try giving your form, which now has theidattribute ofcat-photo-form, a green background.