CSS
body,
html {
width: 100%;
height: 100%;
overflow: hidden;
background: #FFF;
}
a {
width: 300px;
height: 100px;
font-size: 50px;
margin: auto;
line-height: 100px;
text-decoration: none;
position: absolute;
top: 0;
bottom: 0;
left: 0;
right: 0;
display: block;
border: solid 1px black;
text-align: center;
font-family: Arial, sans-serif;
text-transform: uppercase;
color: #666;
transition: all 500ms;
-webkit-transition: all 500ms;
-moz-transition: all 500ms;
z-index: 1;
}
a:after,
a:before {
display: block;
background: #333;
width: 0;
height: 100px;
content: "";
position: absolute;
-webkit-transition: all 500ms;
-moz-transition: all 500ms;
-ms-transition: all 500ms;
-o-transition: all 500ms;
transition: all 500ms;
z-index: -1;
}
a:after {
bottom: 0px;
left: 0px;
width: 50%:
}
a:before {
top: 0px;
right: 0px;
}
a:hover:after,
a:hover:before{
width: 100%;
}
