Resolve "Iteration list background color wrong"

What does this MR do?

Make iteration list look more like regular content list. Needs startup_css enabled (either set the cookie, or add ?startup_css=true to query params

Screenshots (strongly suggested)

before	after

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides

Related to #273552 (closed)