Update cookie consent banner styling to align with brand theme

[TomGreener91]

This commit addresses the issue to improve the look and feel of the cookie banner to be more on brand.

We are utilizing vanilla-cookieconsent, and to customize the UI correctly, I've overridden its internal CSS variables (--cc-*) inside the :root pseudo-class in src/index.css. This links the cookie consent banner to the custom brand variables defined in the Tailwind v4 @theme block.

This updates background colors, primary accent colors, borders, and typography so the banner seamlessly matches the rest of the application without touching any logic or text strings.

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PR created automatically by Jules for task 5207412527614896639 started by @TomGreener91

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Visit the preview URL for this PR (updated for commit a500665):

https://rexvelocity--pr7-jules-cookie-banner-ojsunx20.web.app

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