话不多说，先上图：
代码：
<html>
<head>
<meta content = "text/html,charset=utf-8" >
<style>
html,body{
margin:0px;
padding:0px;
}
#parent{
margin: 0px auto;
height: 30px;
width: 700px;
margin-top: 360px;
position:relative;
}
.child{
position:relative;
float:left;
width:150px;
height:30px;
line-height:30px;
margin-left:10px;
border: 1px solid #9a9797;
cursor:pointer;
text-align: center;
}
.child:before{
content: '';
display: block;
position: absolute;
box-sizing: border-box;
border: 1px solid transparent;
width: 0;
height: 0;
bottom: 0;
right: 0;
-webkit-transition: border-color 0s ease-in 0.4s,width 0.2s ease-in 0.2s,height 0.2s ease-in;
transition: border-color 0s ease-in 0.4s,width 0.2s ease-in 0.2s,height 0.2s ease-in;
}
.child:hover:before {
width: 100%;
height: 100%;
}
.child:hover:before {
border-bottom-color: #367dff;
border-left-color: #367dff;
-webkit-transition: border-color 0s ease-out 0.4s,width 0.2s ease-out 0.4s,height 0.2s ease-out 0.6s;
transition: border-color 0s ease-out 0.4s,width 0.2s ease-out 0.4s,height 0.2s ease-out 0.6s;
}
.child:after{
content: '';
bottom: 0px;
display: block;
position: absolute;
box-sizing: border-box;
border: 1px solid transparent;
width: 0;
height: 0;
top: 0;
left: 0;
-webkit-transition: border-color 0s ease-in 0.8s,width 0.2s ease-in 0.6s,height 0.2s ease-in 0.4s;
transition: border-color 0s ease-in 0.8s,width 0.2s ease-in 0.6s,height 0.2s ease-in 0.4s;
}
.child:hover:after {
width: 100%;
height: 100%;
}
.child:hover:after {
border-top-color: #367dff;
border-right-color: #367dff;
-webkit-transition: width 0.2s ease-out,height 0.2s ease-out 0.2s;
transition: width 0.2s ease-out,height 0.2s ease-out 0.2s;
}
</style>
</head>
<body>
<div id = "parent">
<div class = 'child'>sixgod</div>
<div class = 'child'>sixgod</div>
<div class = 'child'>sixgod</div>
<div class = 'child'>sixgod</div>
</div>
<body>
</html>