Swagger UI 3.0.0 was released on 18 March 2017 and brings a full rewrite of the UI from the ground up.
In this version, they've changed the directory structure to being flat with only a couple of files left.
This means the CSS and JS files are now located in the root of the folder and most files have been merged or removed.
Swagger2Feature contains an internal SwaggerUIResourceFilter that checks for files in these (no longer existing) subfolders, but does not find the new location of (for example) css files.
The pattern it uses is:
This no longer works, since it doesn't allow for files (other than JS and ICO) to be in the root folder.