Transferred one file to iCloud Drive and it showed at the iCloud »
www.icloud.com/#iclouddrive web site
I then transferred 20 files and three folders, with files in them, from DropBox folder in Finder to the iCloud Drive folder. Went to the web and there were three folders (with out any files in them) and only the one file from before was there.
Transferred everything back from iCloud Drive back to DropBox. Went to dropbox.com and all the files were there...instantly
DropBox -1
iCloud Drive -0