Before ending this chapter, we must get some things clear. Bootstrap offers some helper classes mixins and some vendor's mixins, which offer cross-browser compatibility support.
Bootstrap 3 started using box-sizing: border-box for all elements and pseudo-elements. With this enabled, the width and height properties start to include the padding and the border but not the margin.
With that, it is easier to set the right sizing for your elements. This is because any change that you make in the element, such as customizing the padding of a .row, will reflect the width and height of the whole element. The following figure shows you the differences of box-sizing.
