I found an issue that occurs with iphone and iMac using Safari, running on Magento v2.3.1
Steps to reproduce the problem:
1. Visit webpage with iPhone/iMac with Safari browser
2. Tap on Responsive Menu
3. Responsive Menu Opens
4. Tap on Category (i.e "How to buy" in my case), the background page shifted up unexpectedly (see the second screenshot attached below, yellow bordered)
(expected result: the background page should remain as top position)
Any clue to fix this problem? thanks.