Modèle de boites:

 _______________________________________
|           margin (transparent)        |
|   _________________________________   |
|  |        border                   |  |
|  |   ___________________________   |  |
|  |  |     padding               |  |  |
|  |  |   _____________________   |  |  |
|  |  |  |  content            |  |  |  |
|  |  |  |_____________________|  |  |  |
|  |  |___________________________|  |  |
|  |_________________________________|  |
|_______________________________________|

        |    element width    |
|              box width                |