Why does the background picture in the topmost section twitch when I scroll up FROM MOBILE?

Question

css

When scrolling up the site from mobile, the background image in the topmost section seems to twitch testing.internet-24.ru . it's not clear what's going on..

Answer 1

because bg-size:cover and on the phone, when scrolling up, additional menu bars appear, usually at the top and bottom, which reduces the height of the browser display, from which the image starts to rebuild to the new height.