body {
  background-color: lightgray;
}
.book {
  background-color: lime;
  color:white;
  padding: 2px;
}
.qrcode {
  background-color: blue;
  color:white;
  padding: 2px;
}
.friends {
  background-color: orangered;
  color:white;
  padding: 2px;
}
.bill {
  background-color: aqua;
  color:white;
  padding: 2px;
}
a:link { text-decoration: none; }
a:visited { text-decoration: none; }

@keyframes blinking {
  0% { background-color: red; }
  50% { background-color: transparent; }
  100% { background-color: red; }
}

.blinking-link {
  animation: blinking 1s infinite;
  padding: 3px;
}