Here is the custom css I use for my ipython notebook. It is not finished but I think it is a great improvement from the default, the biggest change being that I removed the In/Out prompt. There are some changes to the margins and colours too, and a red dotted line is drawn around running cells. The font for the code was changed to Inconsolata-bz (you need to install that font to get exactly the same look).
To use this custom css as default, first create an ipython default profile:
$ ipython profile create
Create the directory that will contain the custom.css file:
$ mkdir -p ~/.config/ipython/profile_default/static/custom
Save the code below as
custom.css in the directory you just created.
Download the file here: custom.css