#rewards_button {
  display: none;
  position: fixed;
  bottom: 10px;
  right: 10px;
  z-index: 99;
  font-size: 18px;
  border: 1px black solid;
  outline: none;
  background-color: yellow;
  color: black;
  cursor: pointer;
  padding: 10px;
  border-radius: 4px;
}

#rewards_button:hover {
  background-color: black;
  color:white;
}