Update performance bar background color to use the color variables

What does this MR do?

Update performance bar background color to use the color variables

As a part of #299620

Screenshots (strongly suggested)

Stg's performance bar looks slightly different

Type	Before	After
Dev #4c1210 to #4d0a00
Stg #291430 to #14143d
Prod #222222 to #1f1f1f

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team