highlighter: bar highlighter covers the circle highlighter

[markov00]

Describe the bug
I'm not 100% of what is happening here, but I see that the pointer highlighter is partially covered by a semi-opaque layer when mixing bar and line charts.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://elastic.github.io/elastic-charts/?path=/story/axes--custom-domain
2. Slowly move your mouse vertically over the third bar from the left
3. The point highlighter( the bigger circle) get clipped by the bar highlighter or something similar

Expected behaviour
The pointer highlighter should be correctly and fully visible

Screenshots

Version (please complete the following information):

• Browser: chrome
• Elastic Charts: master

Additional context
n/a

[nickofthyme]

Could be related to #1023