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body{
  margin: 0;
  padding: 0;
  background: #f6ff76;
}
a{
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%,-50%);
  width: 200px;
  height: 60px;
  line-height: 60px;
  background: transparent;
  text-align: center;
  text-decoration: none;
  letter-spacing: 4px;
  font-family: sans-serif;
  color: #262626;
  overflow: hidden;
}
a span{
  display: block;
  background: #262626;
  transition: .2s;
}
a span:nth-child(1),
a span:nth-child(3){
  position: absolute;
  height: 2px;
  width: 100%;
}
a span:nth-child(2),
a span:nth-child(4){
  position: absolute;
  height: 100%;
  width: 2px;
}
a span:nth-child(1){
  top: 0;
  left: -100%;
  transition-delay: 0s;
}
a span:nth-child(2){
  top: -100%;
  right: 0;
  transition-delay: .2s;
}
a span:nth-child(3){
  bottom: 0;
  right: -100%;
  transition-delay: .3s;
}
a span:nth-child(4){
  bottom: -100%;
  left: 0;
  transition-delay: .4s;
}
a:hover span:nth-child(1){
  top: 0;
  left: 0;
}
a:hover span:nth-child(2){
  top: 0;
  right: 0;
}
a:hover span:nth-child(3){
  bottom: 0;
  right: 0;
}
a:hover span:nth-child(4){
  bottom: 0;
  left: 0;
}