Err!
Hongkong was given to Britain on lease, when the lease was up, Britain handed over Hong Kong to China....
Learn the history first....
I think Jiu Long (the inner half of Hong Kong) was leased and Hong Kong Island (the outer half) was permanently ceded to Britain. China violated international law and coerced the Britons to return Hong Kong Island upon the lease expiration of Jiu Long. But then again, was colonization ever legal?