🖍 CSS / Styling: Add debug-css-example.html with responsive navbar and ad section

[jokidi717]

✨ What this PR does

This pull request adds a new HTML example file debug-css-example.html with the following:

• A responsive top navigation bar built with embedded CSS
• A clean ad section using a working placeholder image (via.placeholder.com)
• Fully mobile-friendly layout using media queries

🧠 Why it's useful

This contribution improves the styling and structure of the AMP examples by providing a new debug/test case for layout and CSS responsiveness. It can help others trying to create or test custom layouts in AMP environments.

🖼️ Visual Summary

No major visual components added to the site; this is an example file intended for dev use.

📝 Notes

• This PR does not close any open issues.
• Based on feedback, the image was replaced with a working placeholder image source.

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