Describe the bug
The Right or Left legend positions do not account for the browser scrollbar. Particularly, with short legend names.

Only on Chrome and Safari, not FireFox.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://elastic.github.io/elastic-charts/?path=/story/small-multiples-alpha--grid-lines&knob-Show Legend=true
2. Toggle the legend with the provided knob
3. Notice the legend item labels are truncated due to the scroll bar.

Expected behavior
Somehow account for the scrollbar width when legend values exceed the height of the legend container.

Screenshots

When the legend container is set to overflow-x: hidden the issue goes away

Kibana Cross Issues
elastic/kibana#94596