Hi,
1 I added your code to Global Cusom CSS. But the image was still there.
Check: https://ibb.co/2KqHcGW
Link: https://www.advanmart.com/de-thi-starters-doc-va-viet-nang-cao
2 What is the difference if I activate different child themes? I am using the default child theme at the moment. How about the other demo child theme? If I activate them, will they bring more extra functions, pages, etc? Or the only thing different is the home page?