To hit the nail on the head: modify the bootstrap-datepicker.js file
Change 10 to 99999999;
Reason: z-index is to set the stacking order of elements. From negative to positive means stacking from bottom to top. Here, the css method is used to set z-index to 10, and it is an inline style, which cannot be modified using a style sheet.
Summary: The method is very simple, but the process of finding the cause is very complicated. It took me a long time to find a relatively simple solution. Friends who have the same needs can refer to it. I hope you all like it.