Change the code on a shopify website

I am looking for a Shopify expert to make both design and functionality changes to my website. The changes need to be completed ASAP.

Specific requirements:
- Implement design changes to enhance the overall look and feel of the website
- Make functionality changes to improve user experience and optimize site performance

Ideal Skills and Experience:
- Proficiency in Shopify development and customization
- Strong understanding of HTML, CSS, and JavaScript
- Experience in implementing responsive design and mobile optimization
- Ability to work quickly and efficiently to meet tight deadlines

Please provide examples or references for the changes you want, as it will help me better understand your vision and requirements.