feat(ui): Rework theming system, add new theme.

[bastienwirtz]

Description

Rework the style organization to make possible to define colors using CSS variable (instead of only in the yaml configuration), making possible to . Also leverage css @layer to make it easier to override styles in theme or custom CSS stylesheet.

Added features:

• Customize colors using CSS variables
• Add custom css classes on a item groups.
• Finally integrate @walkxcode great theme!

Fixes #305 #398 #406

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

It might break some theming customization, but it should be minimal.

Checklist:

• I've read & comply with the contributing guidelines
• I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• I have made corresponding changes to the documentation (README.md).
• I've checked my modifications for any breaking changes, especially in the config.yml file

[netlify]

✅ Deploy Preview for homer-demo-content ready!

Name	Link
🔨 Latest commit	529fa64
😎 Deploy Preview	https://deploy-preview-789--homer-demo.netlify.app

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[walkxcode]

🥳