header image size

is there a way to customize the size of the header/logo image for gridmarket?

so it does not have to be 980x100

my logo is only 272x100

when i upload an image and choose this image size even though the height is 100px it still wants to crop it at 1/4 the height.

in the grid.css i only see 1 thing related to the size of the header

#header{padding:10px 0px;margin:0px auto;width:980px;}

so i uploaded this to custom.css
#header{padding:10px 0px;margin:0px auto;width:272px;}

but how do i set the theme to use custom.css