Fix Product Page Layout & Add Custom Text Box

My website's product pages are having responsive design issues. These need to be fixed to ensure a seamless user experience across different devices. Furthermore, I need a freelancer to add a text box for customs on these pages.

Ideal skills for this project include:
- Web Design
- Responsive Design
- E-commerce Website Development
- UI/UX Design

Please provide examples of your previous work related to web design and responsive troubleshooting. A keen eye for detail and a good understanding of e-commerce design principles will be crucial for this project.