longpressbutton.css

.lpb-button {
  display: inline-block;
  position: relative;
  appearance: none;
  -moz-appearance: none;
  -webkit-appearance: none;
  overflow: hidden;
  user-select: none;
}

.lpb-button .lpb-loader {
  position: absolute;
  background-color: black;
  border-radius: inherit;
  border-style: none;
  border-color: none;
  opacity: 0;
  height: 100%;
  width: 100%;
  left: 0;
  right: 0;
  top: 0;
}

.lpb-button .lpb-loader.lpb-loading {
  animation-duration: 2s;
  animation-name: loading;
}

.lpb-button .lpb-loader.lpb-loaded {
  animation-fill-mode: forwards;
  animation-duration: 200ms !important;
  animation-name: loaded;
}

@keyframes loading {
  0% {
    opacity: 0%;
  }
  100% {
    opacity: 50%;
  }
}

@keyframes loaded {
  0% {
    opacity: 50%;
    color: black;
  }
  50% {
    opacity: 70%;
    color: white;
  }
  100% {
    opacity: 0%;
    color: black;
  }
}