Sign 3: No dismiss button.
An error alert covers part of the form. User fixes the error. The alert stays. They're not sure if the fix worked or if the alert is still relevant.
Tell AI:
- Dismiss X button: 20px, top-right corner, padding 4px, opacity 0.5 default, 1.0 on hover
- Click: slides up fades out, 200ms, then removes from DOM
- Persistent alerts (critical errors): no dismiss - add an explicit action button instead
- Auto-dismiss (toasts only): 4000ms for success, 6000ms for info, no auto-dismiss for error or warning