CSSCOPY

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(246, 41%, 21%);
  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: translate(50%, -50%) scale(0);
  transition: transform 0.45s ease-in-out;
}

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

button:hover::before {
  transform: translate(50%, -50%) scale(15);
}