Why are the 24 solar terms viewed according to the days of the solar calendar?

Accurately speaking, the ancient calendar in China was the lunar calendar. The ancients said that the moon circled the earth once in January, and the earth circled the sun once in a year. The ancients found that the astronomical year was not only 12 months, so leap months were used to adjust it. The twenty-four solar terms calculated by the ancients divided the earth's time around the sun into 24 minutes on average. The shortest day is the winter solstice, the longest day is the summer solstice, and the day and night are the vernal equinox and autumn equinox. So the 24 solar terms have no fixed date in the lunar calendar, but they are relatively fixed in the western calendar. But because of the leap year, it is not absolutely fixed. You can check it when you have time!