#back-to-top {position:fixed;bottom:5%;left:95%;}
#back-to-top a {text-align:center;text-decoration:none;color:#979797;display:block;width:50px;/*使用CSS3中的transition属性给跳转链接中的文字添加渐变效果*/-moz-transition:color 1s;-webkit-transition:color 1s;-o-transition:color 1s;}
#back-to-top a:hover {color:#4394BB;}
#back-to-top a span {display:block;height:50px;width:50px;background:url(../images/arrow.png) no-repeat center center;margin-bottom:5px;-moz-transition:background 1s;-webkit-transition:background 1s;-o-transition:background 1s;}
#back-to-top a:hover span {background:url(../images/arrow.png) no-repeat center center;}