<style>

header {
    color:white;
    clear:both;
    text-align:center;
    padding:5px;
    border:5px solid red;
}
nav {
    color:white;
    clear:both;
    text-align:left;
    padding:5px;
    border:0px solid red;
}
section {
    float:left;
    padding:5px;
    /*color:#5b5b5b; */
    font-size:80%;
    /*background-color:#efefef; */
    background-color:white; 
    border:0px solid #E6E6E6;     
}
footer {
     /*background-color:#D9D9D9; */
    background-color:#efefef; 
    color:black;
    clear:both;
    text-align:left;
    padding:5px;
    font-size:60%;
}

a{text-decoration: none;}
/* :link 链接默认展示
    :visited 访问过后
    :hover 鼠标悬停
    :active 鼠标按下 */
a:link{color: black;}
a:visited{color:black;}
a:hover{color:green;}
a:active{color:orange;}


</style>
