a:link {color: black; text-decoration: none} /* 未访问的链接 */
a:visited {color: black; text-decoration: none} /* 未访问的链接 */
a:hover {color: blue; text-decoration: none} /* 鼠标在链接上 */
a:active {color: red; text-decoration: none} /* 激活链接 */