I am a little confused. Did you use a tikz editor/assistant that they have? Or did you type your tikz just like you would with ed/vim/emacs? I did not see anything that would assist with creating tikz illustrations when I was poking around. Lowering the tikz bar would be awesome.
If this type of stuff interests you, make sure you check out http://texample.net/tikz/examples/all/ & http://tex.stackexchange.com too. Also, if you want to try and play around with it, use the "Create A New Paper" link @ https://www.writelatex.com/docs?template=paper
Here's the code I'm using: