<button></button>

body {
	display: flex;
	justify-content: center;
	margin: 0;
	height: 100vh;
	background: #dcdcdc;
}

button {
	align-self: center;
  border: none;
  padding: .625em;
  width: 1.75em; height: 1.75em;
  border-radius: 50%;
  box-shadow: 0 1px .125em #444, 
    inset 0 1px .125em #fff;
  background: 
    radial-gradient(transparent 35%, #444) 
      50% calc(50% + .125em) content-box, 
    linear-gradient(#bbb, #bbb) content-box, 
    linear-gradient(#d0d3d5, #d2d5d7);
  background-size: 175% 175%, 
		100% 100%, 100% 100%;
	font-size: 2em;
	cursor: pointer;
}