As someone just getting into web development I've wondered the same thing. Web design frameworks seem to have all these wonderful designs but they're just not fulfilled of fleshed out as Art Nouveau or such ... but of course you can't just sort of copy and paste or you get all kinds of distracting elements.

Still there has to be a place / way this can be done. I've been trying to just use posters I like, starting with color patterns and such to get a feel for such things. I'm a noob so it's all elementary kinda attempts but there it feels like it should be doable.