<body>
  <a href="#">push
    <span></span>
    <span></span>
    <span></span>
    <span></span>
  </a>
</body>
* {
  box-sizing: border-box;
}
body {
  margin: 0;
  padding: 0;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: #999;
}

a {
  border-radius: 12px;
  border: 3px outset #888;
  position: relative;
  display: inline-block;
  padding: 15px 30px;
  color: #eee;
  text-transform: uppercase;
  letter-spacing: 4px;
  overflow: hidden;
  
  box-shadow: 0 0 10px rgb(0, 0, 0, 1);
  font-family: verdana;
  font-size: 28px;
  font-weight: bolder;
  text-decoration: none;
  background:linear-gradient(160deg, #666, #444);
  text-shadow: 0px 0px 2px rgba(0, 0, 0, .5);

  transition: 0.2s;

}
a:active {
  border: 3px outset #ddd;
  color: #fff;
  background: linear-gradient(160deg, #666, #444);
  text-shadow: 0px 0px 4px #ccc;
  box-shadow: 0 0 10px #fff, 0 0 40px #fff, 0 0 80px #fff;
  transition-delay: 1s;
}

a span {
  position: absolute;
  display: block;
}

a span:nth-child(1) {
  top: 0;
  left: -100%;
  width: 100%;
  height: 2px;
  background: linear-gradient(90deg, transparent, #eee);
}
a:active span:nth-child(1) {
  left: 100%;
  transition: 1s;
}
a span:nth-child(2) {
  top: -100%;
  right: 0;
  width: 2px;
  height: 100%;
  background: linear-gradient(180deg, transparent, #eee);
}
a:active span:nth-child(2) {
  top: 100%;
  transition: 1s;
  transition-delay: 0.25s;
}
a span:nth-child(3) {
  bottom: 0;
  right: -100%;
  width: 100%;
  height: 2px;
  background: linear-gradient(270deg, transparent, #eee);
}
a:active span:nth-child(3) {
  right: 100%;
  transition: 1s;
  transition-delay: 0.5s;
}

a span:nth-child(4) {
  bottom: -100%;
  left: 0;
  width: 2px;
  height: 100%;
  background: linear-gradient(360deg, transparent, #eee);
}
a:active span:nth-child(4) {
  bottom: 100%;
  transition: 1s;
  transition-delay: 0.75s;
}

External CSS

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External JavaScript

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