[Theme : twentyfourteen] Increase post width in wordpress blog

I’ve been trying to increase the width of the post container in my theme.
The thing is that, I can’t seem to get it working. I’ve tried editing my style.css, but it just doesn’t work.

I have added a RIGHT sidebar via “STYLE” plugin.

Here are the screen shots to my page :-

http://i.imgur.com/OdM5f8e.png

View post on imgur.com

ohh.. and while you are at it.. please look at this one too :-
https://wordpress.org/support/topic/linking-images-with-the-post-on-homepage?replies=1