This is a good question. I think when writing websites you will always need to know how HTML, CSS work. It is just part of job=). What OJ is trying to do differently is make parts of your website self contained into objects.
So think more, what if I could bundle a part of my website into ShoppingCartView, or HeaderBarWithLoginView? It doesn't remove the HTML and CSS it just simplifies how it is created because OJ Objects create themselves, and once created they modify themselves. Clearly to write these objects you will still need to use and know HTML and CSS, but this provides a different way of encapsulating things.
So think more, what if I could bundle a part of my website into ShoppingCartView, or HeaderBarWithLoginView? It doesn't remove the HTML and CSS it just simplifies how it is created because OJ Objects create themselves, and once created they modify themselves. Clearly to write these objects you will still need to use and know HTML and CSS, but this provides a different way of encapsulating things.