Themelet

Themelet is a term used in web design and blogging communities to describe a small, focused variation of an existing theme. Unlike a full theme, a themelet is designed to be used in conjunction with a base theme, providing modest visual or behavioral changes without restructuring the entire design.

On platforms such as Tumblr, themelets were popular for allowing users to customize appearance by modifying a base theme with custom CSS, HTML templates, and minor JavaScript changes. A themelet typically relies on the base theme's layout and assets but overrides selectors, introduces a color scheme, typography, or header/footer tweaks. It is usually not a standalone product; it requires the base theme to render properly.

Development and distribution: Themelets are created by third-party designers and shared via theme marketplaces or community repositories. They commonly include installation instructions, compatibility notes, and licensing information. Because they depend on a specific base theme version, compatibility may vary across updates; maintainers often release updates to adapt to changes in the underlying theme.

See also: child theme, CSS override, skin, Tumblr theme.