css实现了hover显示title的效果

<div data-title="hello, world">hello...</div>

<style>
div {
    position: relative;
}
div:hover::after {
    content: attr(data-title);    //取到data-title属性的值
    display: inline-block;
    padding: 10px 14px;
    border: 1px solid #ddd;
    border-radius: 5px;
    position: absolute;
    top: -50px;
    left: -30px;
}

</style>

效果如下图：