Sharepoint 2019 Server - issue uploading to Style Library

We're running a Sharepoint 2019 server farm. 

We have one user assigned as Site Owner who is receiving a permissions error when they try to upload to the Style Library.  They were able to create a CSS folder within the Library but are unable to upload content to the folder.  Most of the suggestions I have found apply to Sharepoint online.  

Any suggestions are welcome and appreciated.