Steps to Reproduce

1. load the attached zul with chrome mobile device toolbar to simulate "iPad Pro"
2. scroll down to the button
3. click the combobox button to open its popup

Current Result

the popup appears at the position out of the visible range, you need to scroll down the whole page to see the popup.

Expected Result

the popup shows up at the bottom of the visible range

Debug Info

• datebox also has the same issue.

Root Cause

• <div vflex="1" style="border:solid 5px;overflow:auto"> cause the issue.
• incorrect calculation for "top" at pps.top = jq.px((zk.ios ? window.innerHeight : innerHeight) + scrollOffset[1]); within _syncPosition()
  zk(cave).scrollOffset() adds all scroll offset by iterating every parent elements, which is incorrect for such case. Since page bottom position is not affected by a scrollbar inside an element e.g. <div>

Workaround

• eliminate the scrollbar of the combobox's parent
• calculate it based on scroll position on a page, in _syncPosition()
  pps.top = jq.px((zk.ios ? window.innerHeight : innerHeight) + window.scrollY);