docs: fixed colour scheme after recent doxygen changes

[Jaskowicz1]

The recent doxygen-awesome-css changes changed the colour of warnings and notes. I have rectified it and it is back to how it looked previously.

Documentation change checklist

• My documentation changes follow the docs style guide and any code examples follow the coding style guide.
• I tested that my change works before raising the PR (via running doxygen, and testing examples).
• I have not moved any existing pages or changed any existing URLs without strong justification as to why.
• I have not generated content using AI or a desktop utility such as grammarly.

[netlify]

✅ Deploy Preview for dpp-dev ready!

Name	Link
🔨 Latest commit	83d8d0b
🔍 Latest deploy log	https://app.netlify.com/sites/dpp-dev/deploys/65687c504dd0cb00080462cd
😎 Deploy Preview	https://deploy-preview-1023--dpp-dev.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.