熟悉编写定义各种样式表CSS，练习各种调用样式表的方法：嵌入式样式、链接样式文件、导入样式、内联样式、自定义样式类。-Familiar with the preparation of a variety of defined style sheets CSS, practicing various methods of calling stylesheets: embedded styles, link styles file, import styles, inline styles, cus