CSS data types define typical values (including keywords and units) accepted by CSS properties and functions. They are a special kind of component value type.
The most commonly-used types are defined in the CSS Values and Units specification. This specification also defines functional notations, which allow for more complex types or processing. Other types are defined in the specifications to which they apply.
Below you will find a reference to the types that you are most likely to come across, however it is not a comprehensive reference for all types defined in every CSS specification.