style.css

body {
  margin: 0px;
  font-family: Arial, sans-serif;
  font-size: 80%;
}
#container {
  -moz-user-select: none;
  -webkit-user-select: none;
  user-select: none;
}
#crosshair {
  position: fixed;
  top: 50%;
  left: 50%;
  margin: -2px 0 0 -2px;
  width: 4px;
  height: 4px;
  background-color: #d00;
  opacity: 0.5;
}