469: Improving 404 Page Design and Mobile Responsiveness

[Misakan-tech]

Description of Changes

This PR updates the 404 error page to improve its visual design, accessibility, and responsiveness while ensuring consistency with the DISCOVER Cookbook homepage.

What was improved:

• Replaced the outdated glassmorphism layout with a modern dark theme consistent with the main website.
• Applied DISCOVER brand styling (dark background + green accent).
• Improved mobile responsiveness for better viewing on smaller devices.
• Enhanced accessibility with better contrast and semantic structure.
• Refined messaging to make the page more welcoming and user-friendly.
• Improved button styling for:
  • “Back to Home”
  • “Report the Issue”
• Preserved and enhanced the language switcher functionality.
• Cleaned up layout spacing and typography for better readability.

This update makes the 404 page visually aligned with the rest of the site and improves overall user experience.

Related Issue

Closes #469

Type of Change

• ✨ Content Enhancement — Updates or improves existing content

Additional Notes (Optional)

• The updated page was tested locally and verified on desktop and mobile screen sizes.
• No changes were made to other site components.
• The language switcher retains localStorage functionality.

Checklist

• I have searched open pull requests to avoid duplicates.
• I have built the book locally using the build instructions and verified my changes work as expected.
• I have written clear, conventional commit messages, as per the Pull Request Guidelines.

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[Misakan-tech]

Hi maintainers,

I have updated the 404 page to improve responsiveness and align it with the homepage design as discussed in Issue #469.

Please let me know if any further changes are needed. Thank you!