Widen main/site-main

I have tried( without success) every conceivable css variations to achieve the following: Can the section in yellow on the below page be styled to the full width of the screen? .wrapper{width:100%] expands the whole page which is not what I want. #main and .site-main set to 100% didn't work either. I am trying to achieve parallax effects if that's the right word, i.e. insert a full width image halfway down the page. http://bjbarker.net/mackey/ Hope I'm making sense, Many thanks, bjbarker