[ML] Anomaly explorer timeline doesn't adapt styling when user profile is set to dark theme

[bhavyarm]

Kibana version: 8.8.0 BC6

Elasticsearch version: 8.8.0 BC6

Browser version: chrome latest

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

Describe the bug: Anamoly explorer page displays the viz in white when user profile is set to dark.

Steps to reproduce:

1. go to user profile - edit profile - set to dark
2. Go click on Anomaly explorer
3. Vis part gets displayed in white

Expected behavior:

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[peteharverson]

This looks like an issue with the heat map chart - I also see it in Lens and Dashboard when using a heat map:

[peteharverson]

Note this has been fixed for the Heat Map inside Lens and Dashboard (see #158162) but still needs to be fixed when used inside ML.