Index formatting in online reference
The tree index for the online reference is wrongly formatted on the page: as the tree column is not wide enough, most text in lists is split in multiple lines.  

As it is, it is very difficult to find something scrolling along the tree.
This is a issue for both the latest Firefox (58.0) and Chrome (64.0).
Is it possible to fix the CSS?

This is a screenshot of [https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.to_dict.html](https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.to_dict.html)
![screenshot from 2018-02-21 12-16-36](https://user-images.githubusercontent.com/25978536/36477793-ca84643a-1702-11e8-956c-1624091461af.png)

