[Lens] Embeddable includes White Background When Added to Canvas Workpad

[MichaelMarcialis]

Kibana version:
8.0.0

Elasticsearch version:
8.0.0-SNAPSHOT

Server OS version:
macOS 10.14.6

Browser version:
Chrome 86.0.4240.111

Browser OS version:
macOS 10.14.6

Original install method (e.g. download page, yum, from source, etc.):
From source

Describe the bug:
I noticed that all visualizations added to Canvas workpads have transparent backgrounds by default, except for Lens visualizations (which have a white background). I assume this is a bug.

Steps to reproduce:

1. Create a new Canvas workpad
2. Update workpad settings to have a page background other than white (more obvious on a dark background, like black)
3. Add Element
4. Add from Kibana
5. Select any Lens type visualization

Expected behavior:
I expected Lens visualizations added to a Canvas workpad to have a transparent background, similar to their other visualization counterparts.

Screenshots:

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)