I'm using the debut theme and I added the code for a sticky header. Since I am also using pagefly I had to enter the code into theme.css rather than theme.scss.liquid. I actually got it to work but now it's covering the top of the pages that were just made in shopify. All the fixes for it use theme.scss.liquid which I don't have.
I'm from the PageFly dev team. Please kindly contact us via Live chat so we can access your store to check and fix your issue completely.
We are available 24/7 so you can drop your messages in live chat right now
Do you have your website link? We can look further into this, using page builder is a little more complex than usually. You can also reach out to us https://bit.ly/36CgHKQ.
Looking forward to helping you!