🎨 Palette: Fix button semantics and layout bug

[tonymendonca23]

🎨 Palette: Improved Button Semantics and Fixed Layout Bug

💡 What:

• Converted "Join Us" and "Sign up" buttons from <div> to <button>.
• Added visible focus indicators for keyboard users.
• Fixed a broken layout in the Call to Action section (invalid CSS property).

🎯 Why:

• Accessibility: div buttons are inaccessible to screen readers and keyboard users. Semantic <button> elements provide built-in accessibility features.
• Usability: Keyboard users can now tab to and activate these primary actions.
• Visual Polish: The "Call to Action" section was broken due to a CSS typo, causing elements to bunch up. It is now properly spaced.

♿ Accessibility:

• Added semantic <button> tags.
• Added :focus-visible styles with high contrast outlines.
• Ensured button text remains legible and styled consistent with the design.

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PR created automatically by Jules for task 2088962325373582914 started by @tonymendonca23

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