Hello Yichong,
My understanding about the project is that you need certain specific tweaks to be conducted on your existing website. Kindly send us your project brief and share your website URL with us for our better understanding.
Relevant Shopify Skills:-
1. Theme Customization
2. Admin Interface
3. Product Management
4. E-commerce Marketing
5. Web Hosting and Analytics
If you are available right now, let's have a chat to discuss further details regarding "Floating Cart functionality".
Waiting for your valuable reply.