多个浏览器对容器宽度实际像素的解释

IE/Opera

对象的实际宽度 = (margin-left) + width + (margin-right)

Firefox/Mozilla

对象的实际宽度= (margin-left) + (border-left-width) + (padding- left) + width + (padding-right) + (border-right-width) + (margin-right)