SOURCE

<button>Button</button>

button{
    z-index: 1;
    position: relative;
    font-size: initial;
    font-family: initial;
    padding:0.5em 1em;
    color:white;
    outline: none;
    border:none;
    background-color: hsl(236, 32%, 26%);
    overflow: hidden;
    transition: color 0.4s ease-in-out;
}
button:hover{
    cursor: pointer;
    color: #161616;
}
button::before{
    content: '';
    z-index: -1;
    position: absolute;
    top:50%;
    left:50%;
    width: 1em;
    height: 1em;
    border-radius: 50%;
    background-color: #3cefff;
    transform-origin: center;
    transform: translate3d(-50%,-50%,0) scale3d(0,0,0);
    transition: transform 0.45s ease-in-out;
}
button:hover::before{
    transform: translate3d(-50%,-50%,0) scale3d(15,15,15);
} 

 /* button {
  z-index: 1;
  position: relative;
  font-size: inherit;
  font-family: inherit;
  color: white;
  padding: 0.5em 1em;
  outline: none;
  border: none;
  background-color: hsl(236, 32%, 26%);
  overflow: hidden;
  transition: color 0.4s ease-in-out;
}

button::before {
  content: '';
  z-index: -1;
  position: absolute;
  top: 100%;
  right: 100%;
  width: 1em;
  height: 1em;
  border-radius: 50%;
  background-color: #3cefff;
  transform-origin: center;
  transform: translate3d(50%, -50%, 0) scale3d(0, 0, 0);
  transition: transform 0.45s ease-in-out;
}

button:hover {
  cursor: pointer;
  color: #161616;
}

button:hover::before {
  transform: translate3d(50%, -50%, 0) scale3d(15, 15, 15);
}  */