You need to edit several classes:

body{margin: 0; padding:0; } --> removes some of the space between canvas and navigation strip

#canvas{margin: 0; padding: 0; overflow: hidden; } --> makes the whole canvas box 'visible', thereby 'removing' the space between header and navigation strip

#canvas .inner{margin: 0; padding: 0; overflow: hidden;} --> removes space between header and top of canvas box and and top of content box

Hope this works for you as well!