There is only one file type that uses the .WEBTHEME extension:
iWeb Theme Template
Theme template created by iWeb, a user-friendly Web design program; contains pre-designed themes such as Leaf Print, Fine Line, Goldenrod, and Modern Frame; each theme contains fonts and images specific to the theme; opened through the application.
NOTE: iWeb was part of Apple's iLife application suite.
|Apple iWeb — Discontinued||Paid|
Updated: August 6, 2013