webextensions-examples/beastify/popup/choose_beast.css

html, body {
  width: 100px;
}

.button {
  margin: 3% auto;
  padding: 4px;
  text-align: center;
  font-size: 1.5em;
  cursor: pointer;
}

.button:hover {
  background-color: #CFF2F2;
}

.beast {
  background-color: #E5F2F2;
}

.clear {
  background-color: #E74C3C;
}

.clear:hover {
  background-color: #C0392B;
}