Radio Schedules: Change full width background colour of section to Lunar

[tochwill]

Is your feature request related to a problem? Please describe.
When we have displayed radio schedules on the front page, and have the ability to create a full width section, we should change the background colour of the radio schedules section to Lunar (#f2f2f2).

Ensure that the section label is displayed correctly on this background colour.

Zeplin link: https://app.zeplin.io/project/5c8a5e021d454124ef90669f/screen/5e1cb5109da20e0404f7f0ec

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Testing notes
[Tester to complete]

Dev insight: Will Cypress tests be required or are unit tests sufficient? Will there be any potential regression? etc

• This feature is expected to need manual testing.

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[tochwill]

Blocked on #5760