style: modernize 404 page UI

[Aditya30ag]

Description of Changes

This Pull Request modernizes the 404 (Not Found) page UI by migrating all custom CSS to Tailwind CSS utilities.
The update improves visual consistency, readability, and responsiveness while preserving all existing functionality.

Key improvements include:

• A clean, modern layout with improved spacing and typography
• Tailwind-based glassmorphism styling and subtle ambient gradients
• Clearer visual hierarchy with emphasis on the 404 error state
• Improved button and language selector styling
• No changes to language detection or translation logic

This change makes the page easier to maintain and more consistent with modern UI standards.

---

Related Issue

Closes #469

---

Type of Change

Please check the appropriate box that describes your PR:

• 🐛 Bug Fix — Fixes a documented issue or incorrect behavior
• ✨ Content Enhancement — Updates or improves existing content
• ✍️ New Content — Adds new chapters, examples, or significant sections
• 🛠️ Other — Please describe in the Description of Changes section

---

Additional Notes (Optional)

This update focuses purely on UI/UX improvements.
No functional or behavioral changes were introduced.
Screenshots can be added if required for review.

---

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.

[netlify]

❌ Deploy Preview for stupendous-kringle-a86e81 failed.

Name	Link
🔨 Latest commit	6cf46f6
🔍 Latest deploy log	https://app.netlify.com/projects/stupendous-kringle-a86e81/deploys/69a058102ed4c30008d16746

[Aditya30ag]

[Aditya30ag]

@OriolAbril Please have a look

[AR21SM]

Hi @Aditya30ag Could you please update this to use Bootstrap instead of Tailwind? Also, please add automatic light/dark theme support that respects the user's system preferences.
The current implementation uses Tailwind's Play CDN which isn't suitable for production. Bootstrap would be a better fit for this project.
Thanks!

[Aditya30ag]

ok got it

[Aditya30ag]

@AR21SM Done the changes please have a look

[AR21SM]

@Aditya30ag

[Aditya30ag]

Sorry I will fix this

[Aditya30ag]

@AR21SM Is this Ok now ?

[AR21SM]

@Aditya30ag fix language. Also, would you be open to using a slightly darker (black) theme, and possibly a simple language toggle instead of a dropdown??

---

[Aditya30ag]

Hey @AR21SM
what the status about this pr

[AR21SM]

@Aditya30ag fix language. Also, would you be open to using a slightly darker (black) theme, and possibly a simple language toggle instead of a dropdown??

@Aditya30ag are you able to made these changes ?

[Aditya30ag]

Hey @AR21SM,

sorry for late response
i had done the changes please have a look

[Aditya30ag]

@AR21SM please have a look

[AR21SM]

Kindly squash the commits into a single commit

[AR21SM]

@aterrel can you take a look

[Aditya30ag]

@AR21SM successfully squash the commit