Use Hosted accent colour for lightbox divider

[cemms1]

What does this change?

• Moves the accent colour overrides function to a different file for easier re-use
• Uses the accent colour of the hosted content campaign for the lightbox divider
• Ensures the other palette colours using the accent colour come through to the HostedGalleryLayout component
• Adds a storybook variation for hosted content with accent colour

Why?

We want the lightbox divider colour to be the same as the accent colour of the hosted content campaign.

This is part of the Hosted Content migration from frontend to DCR

Screenshots

Before	After

[github-actions]

Deploy build 28368 of dotcom:rendering-all to CODE

All deployment options

• Deploy build 28368 of dotcom:rendering-all to CODE
• Deploy parts of build 28368 to CODE by previewing it first
• What's on CODE right now?

---

From guardian/actions-riff-raff.