demo.css

iframe {
  border: none;
}
.button {
  border-radius: 30px;
  border: 2px outset gray;
  width: 296px;
  height: 146px;
}
#freebeer {
  background-image: url(img/beer.png);
  background-color: white;
  background-size: contain;
  background-position: center;
  background-repeat: no-repeat;
  display: flex;
  flex-direction: column;
  justify-content: center;
}
#freebeer::after {
  content: "Free beer!";
  text-align: center;
  font-family: sans-serif;
  font-size: 56px;
  font-weight: bolder;
  color: red;
  animation-name: blink;
  animation-duration: 1s;
  animation-timing-function: steps(2);
  animation-iteration-count: infinite;
  animation-direction: normal;
  animation-play-state: running;
}
#response {
  display: inline-block;
  font-size: 36px;
  text-align: center;
  border: 1px solid black;
}
@keyframes blink {
  0% {
    visibility: visible;
  }
  50% {
    visibility: hidden;
  }
}