本文介绍了盒子模型与标准文档流的概念，阐述了盒子在标准流中的定位原则。重点解析了CSS 中的浮动属 性，并通过具体的网页布局实例进一步说明浮动属性的用法。

This paper introduces the conception of box-model and normal document stream, and states the position principle of box in normal document stream. It analyzes the float attribute of CSS, and gives the method of using float by specific case.