.join-btn {
  background-color: #ff0000;
  color: #ffffff;
  font-size: 24px;
  font-weight: bold;
  padding: 22px 70px;
  border: none;
  border-radius: 5px;
  cursor: pointer;
  position: relative;
  overflow: hidden;
}

.join-btn:before {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  width: 0;
  height: 0;
  background-color: rgba(255, 255, 255, 0.2);
  border-radius: 50%;
  transform: translate(-50%, -50%);
  transition: width 0.3s ease-out, height 0.3s ease-out;
}

.join-btn:hover:before {
  width: 300px;
  height: 300px;
}

.join-btn:focus {
  outline: none;
}