Better to avoid
A stolen mouthful won’t hurt, but cats must not live on dog food. It lacks taurine and other nutrients cats need, and a long-term dog-food diet causes serious illness.
Dogs are omnivores; cats are obligate carnivores with stricter needs. Cat food is specially fortified with taurine (an essential amino acid cats cannot make enough of), more protein, vitamin A in a usable form, and arachidonic acid. Dog food lacks adequate taurine — a chronic deficiency causes heart disease (dilated cardiomyopathy) and blindness in cats. In multi-pet homes the occasional nibble from the dog’s bowl is harmless; the danger is feeding dog food as a cat’s regular diet.
None as a diet. If your cat occasionally steals dog kibble, do not panic — just make sure their own complete cat food is what they actually live on. Feed pets separately if your cat is a habitual bowl-raider.
Always feed a complete, cat-specific food. For treats, plain chicken beats any dog product.
Related: Can cats eat chicken? · Can cats eat bread? · Can cats drink milk?
General information, not veterinary advice. If your pet has eaten something potentially harmful or shows symptoms, contact your vet or an emergency clinic immediately. Full disclaimer.