An absolute position element is positioned relative to the first parent element that has a position other than static
Absolutely positioned elements are removed from the normal flow.
absolute 位置是相对第一个具有position(fixed, relative, absolute) 属性的父元素位置, 实际位置可能和DOM中的不一致(be removed from the normal flow)。
CSS 中 Position relative 和 absolute区别
原文：http://www.cnblogs.com/happylong/p/4501387.html