#captcha {
  user-select: none;
  background-color: #C0C0C0;
  width: 150px;
  height: 60px;
  font-size: 30px;
  font-weight: bold;
  display: inline-block;
  padding: 15px 4px;
  text-align: center;

  -webkit-text-stroke: 1px black;
  color: white;
  text-shadow: 3px 3px 0 #000, -1px -1px 0 #000, 1px -1px 0 #000,
    -1px 1px 0 #000, 1px 1px 0 #000;

}

#userInput, #rtn{
  margin: 5px 0px;
}

#arithmetic_cal{
  width: 100px;
  height: 30px;
  font-size: 20px;
  display: inline-block;
}


@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}


.spin-rotate {
  animation: spin 1s linear infinite;
}