Hi @AllyC, this is not officially supported yet in Webflow, but if you’re feeling brave you can manually implement this feature using a custom script embed.
We have an example of a 3rd party “affix” plugin in action here:
http://affix-demo.webflow.com/
And the read-only link to the design tool:
https://webflow.com/design/affix-demo?preview=21b1d0b726f25678ca3d3800eea83ce6
Hope that helps!