Gets a style property from this for the given state.
Note that not all CSS properties that are supported by GTK+ can be retrieved in this way, since they may not be representable as Value. GTK+ defines macros for a number of properties that can be used with this function.
Note that passing a state other than the current state of this is not recommended unless the style context has been saved with save.
value is no longer needed, unset must be called to free any
style property name
state to retrieve the property value for
return location for the style property value