It is quite warm now, 25 degrees at daytime, so, it will not be cold in early December. Better to check out the Hong Kong weather(https://www.travelchinaguide.com/climate/hongkong.htm) juest before the day of leaving. That is more accurate report. Need to bring light jacket in case of cold weather and it is a bit cool early in the morning. I recommend Ocean Park, Victoria Peak and the wax museum, get around Central, Wan Chai, Causeway Bay, shopping in Tsim Sha Tsui and see Symphony of Light on Avenue of Stars.