🎨 Palette: Refactor buttons for accessibility

[tonymendonca23]

🎨 Palette: Refactor buttons for accessibility

💡 What:

• Converted "Join Us" and "Sign up" buttons from <div> wrappers containing <h4> tags to semantic <button> elements.
• Updated CSS to preserve visual styling (font-weight, font-family) and added :focus-visible styles for keyboard accessibility.

🎯 Why:

• The previous implementation used non-semantic div elements, making them inaccessible to keyboard users (no tab focus) and screen readers.
• Nested headings (h4) inside "buttons" disrupted the document outline.

📸 Before/After:

• Visually identical.
• Added visible focus ring (white outline) when navigating via keyboard.

♿ Accessibility:

• Added button role.
• Enabled keyboard focus/activation.
• Improved color contrast for focus indicators.

---

PR created automatically by Jules for task 10215509150892168973 started by @tonymendonca23

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.