body{
    margin: 0;
    padding: 0;
    background: #262626;
}
a{
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%,-50%);
    width: 180px;
    height: 50px;
    background: #262626;
    text-transform: uppercase;
    text-align: center;
    line-height: 50px;
    color: #ff0;
    text-decoration: none;
    font-size: 20px;
    font-family: Verdana, Geneva, Tahoma, sans-serif;
    letter-spacing: 4px;
    letter-spacing: 4px;
}
a:before,
a:after,
span:before,
span:after{
    content: '';
    position: absolute;
    width: 10px;
    height: 10px;
    background: #ff0;
    transition: 1s;
    mix-blend-mode: hue;
}
a:before
{
    top: -2px;
    left: -2px;
}
a:after{
    top: -2px;
    right: -2px;
}
span:before{
    bottom: -2px;
    left: -2px;
}
span:after{
    bottom: -2px;
    right: -2px;
}
a:hover:before,
a:hover:after,
a:hover span:before,
a:hover span:after{
    width: calc( 180px / 2);
    height: calc( 50px / 2);
}