Though is doesn't teach you html and css, it is assumed that you are already familiar with all these properties in order to make a good use of it. The application provides you with the facilities to manipulate them easily.
There is no need to embed the whole java runtime environment. As 200MB are too much to download for a simple application. But as I understand that Apple is phasing out all java files from its operating system, so they are encouraging developers to embed the runtime in their applications.
Perhaps the developers can provide 2 versions for download, one with and without the java runtime environment, so that people who have java already installed on their machines can download the slim version.
All in all, it is a good tool for anyone who deals with html documents and website development.