So Allāh is Blessed and Exalted from that evil should be ascribed to him. Rather, everything that is ascribed to him is good. Evil only becomes evil when it ceases to be attributed and ascribed to Him...
There are generalities [shared between them] and specifics [unique to each of them]. Shirk is more general than kufr, for every mushrik is a kāfir but not every kāfir is a mushrik.
The parable of those who disbelieve in their Lord is that their works are as ashes, on which the wind blows furiously on a stormy day, they shall not be able to get aught of what they have earned.