How to remove the white bar at top of screen in Vim?

To recreate, do :set background=dark, and you’ll see it on top of the screen. I’m using the railscasts theme, but I don’t think it has anything to do with that.

Solution

Setting background=dark is not enough to show the tabline, you should start recreation with vim -u NONE.

By default tabline does not appear unless there is more then one tab. This behavior is controlled by showtabline option which defaults to 1. 0 switches off tabline even if there is more then one tab, 2 makes tabline to be shown even if there is only one tab. Try verbose set showtabline? to find out what script replaced showtabline=1 with showtabline=2.