<style type='text/css'>
    body {width:100%;}
</style>

<style type="text/css">
@media screen and (min-width:1px) and (max-width:1365px) {
    ...
}
@media screen and (min-width:1366px) {
    ...
}
</style>

body {width:100%;}

<link rel='stylesheet' media='screen and (min-width: 778px)' href='css800width.css' />