/*effects*/
.btn {
    position: relative;
    z-index: 1;
    overflow: hidden;
    transition: all 0.3s;
}
.btn:after {
    content: '';
    position: absolute;
    z-index: -1;
    -webkit-transition: all 0.3s;
    -moz-transition: all 0.3s;
    transition: all 0.3s;
    width: 100%;
    height: 0;
    top: 0;
    left: 0;
}
.btn:hover:after,
.btn:active:after,
.btn:focus:after{
    height: 100%;
}