Alert

An inline message that stays until the condition changes. For transient confirmation use Toast.

Status variants use a 4% tint and a 32% border of their hue — never a solid fill.
AlertDescription is a flex column, so its children must be block elements — wrap prose in <p style={{margin:0}}>.
Server errors render once, above the form, in an Alert; field errors render on their field. Never both for one submission.