.radioactivity-gauge {
  width: 16px;
  height: 16px;
  display: block;
  background: transparent url(../images/gauge.png) repeat-y 0 0;
}

.radioactivity-gauge.lvl-3 {
  background-position: 0 0;
}

.radioactivity-gauge.lvl-2 {
  background-position: -16px 0;
}

.radioactivity-gauge.lvl-1 {
  background-position: -32px 0;
}