Changing sidebar and content width

Hello everybody, Please, I need some help in my site: I want to know how can I increase the content width and decrease the sidebar width (no matter that then I have to change width of widgets), without changing the separation gap width between both? I have tried to use this code but doesn´t work: @media screen and (min-width: 1225px) { #primary { width: 784px; } #secondary { width: 376px; } } I have seen that margins from both (content and sidebar) fit vertically with featured images slider box size, so If I finally get to change width from both, is there a way to change featured image slider box width as well? And a Finally question, is there a way that I can include a vertical line (or bar) in the separation gap between content and sidebar? Thank you in advance!!