How nice of you: Está correto?

Hello there!!!

Can U help me with a slight doubt that showed up in my head?

I'm an English teacher and I have a student who wrote in his composition the following sentence:

"How nice of you, I'll send you flowers for your kindness"

I guess he meant:
Que gentil de sua parte, eu lhe enviarei flores por sua gentileza

But I'm not so sure if the sentence is really right, cause i've never heard or seen this structure " How nice of you "

Can U help me about it?
Thanks in advance!!!!!