Rule of thumb - if you\'re messing with CSS too much in your layouts, switch to a framework. I\'ve been going over the dozens of grid/layout frameworks out there and most of the
"dozens of grid/layout frameworks out there and most of them focus on the traditional document grid layout."
You make it sound like its a bad thing. I dont see why you would not use a grid framework. It is fairly standard practice if you have any intention what so ever to make your application tablet and mobile friendly. Most of them are extremely quick to setup with little to no extra css required.
Take kube for example. It is very minimalistic and flexible. You basically just add pre defined classes to the div tag you wish to apply as the for the size.
This type of step does not mess with modals or ifames. To modify all you need to do is change the class .. need a larger left hand side, just change the class of the div
This will degrade gracefully for the smaller resolutions while keeping your style of coding as it would be in any other application.
You can write from scratch if you want but .. why?
foundation is also really good and the one i use for my projects