Remember those days when we needed to bust our heads over the wall with plane old box-model in css and actually calculate everything ?
I had to put on paper my padding, margin and border AND width and that would be the actual width of an element ( be it block or inline level one ).
The solution is fairly old but just wanted to share it with you:
-webkit-box-sizing: border-box; /* Safari/Chrome, other WebKit */
-moz-box-sizing: border-box; /* Firefox, other Gecko */
box-sizing: border-box; /* Opera/IE 8+ */
Here is the link for more info : http://css-tricks.com/box-sizing/
Most of the experienced guys would know this , but it is a nifty thing to know if you are a beginner