CSS3制作hover下划线动画

<div>    
    <a href="javascript:void(0);" class="demo1">自己实现的hover效果</a>
</div>

.demo1{
            position: relative;
            text-decoration: none;
            font-size: 20px;
            color: #333;
        }
.demo1:before{
            content: "";
            position: absolute;
            left: 50%;
            bottom: -2px;
            width: 0;
            height: 2px;
            background: #4285f4;
            transition: all .3s;
        }
.demo1:hover:before{
            width: 100%;
            left: 0;
            right: 0;
        }

<div>
    <a href="javascript:void(0);" class="demo2">Hexo next主题的实现</a>
</div>

.demo2{
            position: relative;
            text-decoration: none;
            font-size: 20px;
            color: #333;
        }
.demo2:before{
            content: "";
            position: absolute;
            left: 0;
            bottom: -2px;
            height: 2px;
            width: 100%;
            background: #4285f4;
            transform: scale(0);
            transition: all 0.3s;
        }
.demo2:hover:before{
            transform: scale(1);
        }