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;
  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);
}