[CT-1074] [Feature] Ability to change background color of graph area and node edges (lines)

### Is this your first time submitting a feature request?

- [X] I have read the [expectations for open source contributors](https://docs.getdbt.com/docs/contributing/oss-expectations)
- [X] I have searched the existing issues, and I could not find an existing issue for this feature
- [X] I am requesting a straightforward extension of existing dbt functionality, rather than a Big Idea better suited to a discussion

### Describe the feature

Now that dbt 1.3 will allow us to change node colors, I thought it would be nice if we could also change the background color of the lineage area.

### Describe alternatives you've considered

_No response_

### Who will this benefit?

users of dbt docs.

### Are you interested in contributing this feature?

_No response_

### Anything else?

https://getdbt.slack.com/archives/CKHBDNHA6/p1661355317116189