making masthead/content true full width

I would like to experiment with making this page/site true full-width – currently I can make the header image or the slider full width, but when I try to alter the CSS for the

#page {
max-width: 1180px;
}

to 100% or an alternative pixel value, nothing happens, the container remains 1180 pixels wide

The page I need help with: [log in to see the link]