“CSS4” has no technical meaning whatsoever. All current CSS specifications have their own specific versions ranging from 1 to 4, but CSS as a whole does not have a version, and it doesn’t need one, either.
By using TypeScript's static type system, not only can we enforce (typically challenging things like) business rules and error states, but we can create a domain-specific language so well-defined that it becomes virtually impossible for any future code to be written that puts the system in an illegal state.
Whenever we execute a script, most often we do not think about what happens behind the curtains of our runtime. However, piecing together the bits and pieces to find out what is going on is pretty interesting!