Adding custom styled paragraphs in markdown cells

I want to add more formatting elements than provided by the Markdown synthax in an IPython Notebook.

For example, I want to add a "Warning Box" or a "Memo Box" that are basically paragraph with different styles (for example different background color, border, an icon, etc...).

I guess I can add HTML code in the cell, for example a <div> with an inline style. But what is the "proper" way to do that, I mean the one that ipython developer promote?

Examples appreciated.

NB: I'm using the current 1.0dev version from git master.