btn_hover_circle

by Nic Fontaine

HTML

<div class='btn'>BUTTON</div>

CSS

body {
  text-align: center;
}

div.btn {
  background: #888;
  color: #fff;
  padding: 20px 25px;
  display: inline-block;
  font-family: sans-serif;
  border-radius: 6px;
  cursor: pointer;
  position: relative;
  z-index: 0;
  overflow: hidden;
  transition: background 0.1s 0.1s;
  box-shadow: inset 0 -2px 9px rgba(0,0,0,0.4);
  box-sizing: content-box;
  /* border: 3px solid #666; */
  margin: 20% auto 0;
}

div.btn:hover {
  background: #aaa;
  padding-top: 19px;
  padding-bottom: 18px;
  border-bottom: 3px solid #888;
  text-shadow: 0 1px 1px rgba(0,0,0,0.2);
  box-shadow: 0 2px 2px rgba(0,0,0,0.2);
}

div.btn:before {
  animation: btnGrowNull 0.01s;
}

div.btn:hover:before {
  content: '';
  width: 40px;
  height: 40px;
  background: #aaa;
  position: absolute;
  right: 0; left: 0; top: 0; bottom: 0;
  margin: 0 auto;
  top: 50%;
  transform: translateY(-50%) scale(1,1);
  z-index: -1;
  border-radius: 50%;
  animation-fill-mode: forwards;
  animation: btnGrow 0.15s linear;
  transform-origin: 50% 50%;
  opacity: 0;
}

@keyframes btnGrowNull {
  from { opacity: 0; }
  to { opacity: 0; }
}

@keyframes btnGrow {
  0% { transform: translateY(-50%) scale3d(1,1,1); opacity: 0.5; }
  99% { transform: translateY(-50%) scale3d(4,4,1); opacity: 1; }
  100% { opacity: 0; }
}