Why is the winter solstice a traditional festival in China? Is it really a new calendar?

Winter solstice is one of the 24 solar terms. The solar calendar is a new calendar. The 24 solar terms marked in the China lunar calendar belong to the solar calendar. Because the 24 solar terms are divided according to the changes of the four seasons, which is caused by the period of revolution of the earth, and the solar calendar is formulated according to the period of revolution of the earth. So the date of the 24 solar terms is basically fixed on the solar calendar, so the 24 solar terms belong to the solar calendar.