How do I add a floating navigation bar to my website?

[Kabeer2]

Hello, Can someone please tell me how to add a floating navigation bar which follow through whole website till footer in Shopify. Just like in the attached image & site.

Here is the site link ( please visit it once )

https://www.designjoy.co/

- Thank you so much for you help, means a lot. 

[Kabeer2]

I know i have to write css, but i don't know exactly how to and where to find. can you please provide me css ? thank you