[bug fix] reverted css to fix display bug in documentation, example page

Revert change introduced by @jnothman in 
https://github.com/scikit-learn/scikit-learn/commit/937f36cba77f18af7b37f0798f76aaeaed0b02d8
causing a big empty space in the documentation, on the example page, after the first example

@jnothman, was this line changed to fix another bug somewhere?