Difficult to scroll people list on wide screens

[tmtmtmtm]

When there are a lot of politicians, it's difficult to scroll the list of them as there's no visual distinction between the column they're actually in (where you need to scroll) and the un-scrollable column to the right of it

http://seepoliticianstweet.github.io/Estonia_Riigikogu/areas/tallinna-mustam-e-ja-n-mm.html

[zarino]

Pull request here: https://github.com/mysociety/SeePoliticiansTweet/pull/79