In Jdeveloper by default the auto suggestion of ADF Faces is disabled for the Skin/CSS file. But Jdev provides the option to enable it so that it’ll be easy for us to add the skinning to ADF faces components.
Settings to be done for this: Tools -> Preferences -> CSS Editor -> Check the ADF Faces Extension
After making the above settings open a CSS file and you will be able to see the auto suggest functionality.
Hope this will be useful…