Different behaviour of system scroll in different browsers

I checked "Recycle scroller" demo in three different browsers:
1. **Firefox** — 77.0a1 (2020-04-14) (64-bit)
2. **Microsoft Edge** — Version 84.0.484.0 (Official build) Canary (64-bit)
3. **Safari** — Version 13.1 (15609.2.1)

Please check this video — https://imgur.com/a/oiXRmgZ
Same but GIF:

### Results:
**Firefox** works is expected
**Microsoft Edge** — scroll is invisible at all (of course in Chrome too)
**Safari** — Scroll is inaccessible due to some styling

### Found a solution:
1. Add any positive `z-index` after this line https://github.com/Akryum/vue-virtual-scroller/blob/master/src/components/RecycleScroller.vue#L567
2. Remove these lines — https://github.com/Akryum/vue-virtual-scroller/blob/master/src/components/RecycleScroller.vue#L589-L590

Please check this video for fix — https://imgur.com/a/2h88x9N
Same but GIF: