<style>

/* Tooltips */

[data-tooltip]{position:relative}

[data-tooltip]:before{content:'';visibility:hidden;opacity:0;border:5px solid #000;border-top-color:#000;border-right-color:transparent;border-bottom-color:transparent;border-left-color:transparent;position:absolute;top:-7px;left:10px;z-index:8;font-size:0;line-height:0;width:0;height:0;-webkit-transition:opacity 0.2s;-moz-transition:opacity 0.2s;-o-transition:opacity 0.2s;transition:opacity 0.2s}

[data-tooltip]:after{visibility:hidden;opacity:0;content:attr(data-tooltip);position:absolute;top:-35px;left:0;padding:0 0.5em;background:#000;color:#fff;z-index:9;font-size:13px;height:28px;line-height:28px;white-space:nowrap;word-wrap:normal;-webkit-transition:opacity 0.2s;-moz-transition:opacity 0.2s;-o-transition:opacity 0.2s;transition:opacity 0.2s}

[data-tooltip]:hover:before,[data-tooltip]:hover:after{visibility:visible;opacity:1}

</style>

​

<br /><br /><br />

<a data-tooltip='Mô tả cho thẻ' href='#null'>Demo Tooltips</a>