Maximum page width

HI, Still playing with the theme before moving to the pro version. Site here (very experimental): I have a problem with the maximum page width. It seems to be set at about 1200px when a sidebar is present and diminishes to about 1000px without a sidebar. I would like to make it larger while staying responsive. I would also like to keep the width similar, with or without a sidebar. Searching the forum, I found a suggestion for a Custom CSS but it doesn't seem to work at all: .wrapper { max-width: 1260px; } Is there a way to do this ? If not, can it be done in the Pro theme ? Thanks for your help Jules