Fractional pixel margin rounding issue #407
Description
Margins are rounded to a pixel value before being added resulting in margins sometimes being 1 pixel too wide. For example, if two adjacent elements both have margins of 2.5px, those margins will get rounded to 3 resulting in a total space of 6 pixels between the elements. The correct behavior is to add them before rounding which would result in a total space of 5 pixels.