css3 +data属性实现提示框

a { 
    border-bottom:1px solid #bbb;
    color:#666;
    display:inline-block;
    position:relative;
    text-decoration:none;
}
a:hover,
a:focus {
    color:#36c;
}
a:active {
    top:1px; 
}
 
/* Tooltip styling */
a[data-tooltip]:after {
    border-top: 8px solid #222;
    border-top: 8px solid hsla(0,0%,0%,.85);
    border-left: 8px solid transparent;
    border-right: 8px solid transparent;
    content: "";
    display: none;
    height: 0;
    width: 0;
    left: 25%;
    position: absolute;
}
a[data-tooltip]:before {
    background: #222;
    background: hsla(0,0%,0%,.85);
    color: #f6f6f6;
    content: attr(data-tooltip);
    display: none;
    font-family: sans-serif;
    font-size: 14px;
    height: 32px;
    left: 0;
    line-height: 32px;
    padding: 0 15px;
    position: absolute;
    text-shadow: 0 1px 1px hsla(0,0%,0%,1);
    white-space: nowrap;
    -webkit-border-radius: 5px;
    -moz-border-radius: 5px;
    -o-border-radius: 5px;
    border-radius: 5px;
}
a[data-tooltip]:hover:after {
    display: block;
    top: -9px;
}
a[data-tooltip]:hover:before {
    display: block;
    top: -41px;
}
a[data-tooltip]:active:after {
    top: -10px;
}
a[data-tooltip]:active:before {
    top: -42px;
}

<a href="aasd" data-tooltip="niasdasdasdahao">asdasdasdasdas</a>

效果图：