body {
  margin: 0;
}

body * {
  box-sizing: border-box;
}

.my-button {
  background-color: aqua;
}

body {
  animation-duration: 1s;
  animation-name: hint_open;
}

@keyframes hint_open {
  from {
    background-color: white;
    opacity: 1;
  }

  50% {
    opacity: 0.5;
    background-color: hsl(0, 0%, 88%);
  }

  to {
    background-color: white;
    opacity: 1;
  }
}