What a question, of course! You may be too young to remember the live broadcast from 12 years ago but the July 1, 1997 the British government handed over power to the Chinese government just as it had been stipulated 100 years ago.
The fact is that in 1841 China lost the First Opium War with England and that is why it ended up handing over the island of Hong Kong with a 100-year contract to expire in 1997. And well, the day arrived and both governments negotiated the transfer since Besides being a political transfer, here there were two different systems in play: the capitalist and the communist.
I remember that there were then great discussions and debates about what could happen and what China would do with this capitalist center, but finally everything was adapted with that of "one country, two systems" and there were no major problems. In any case, it is good to know that Hong Kong and also Macao receive special treatment and are called SAR's (by Special Administrative Regions).