'Delivery time exceeded my expectations. Thank you.'
'Thank you for your help; although we left before we saw the flowers, I'm sure they were fine (though I would like to see a picture of them, that is not necessary--it's the thought that counts after all). And the person I talked to on the chat line was very helpful after I placed the order; we discussed the telephone # that I used.'
'Thank you so much!!!'
You won't be able to dismiss this by usual means (escape or click button), but you can close it programatically based on user choices or actions.