.switch-regalo {
  position: relative;
  display: inline-block;
  width: 60px;
  height: 34px;
}

.switch-regalo input {
  opacity: 0;
  width: 0;
  height: 0;
}

.slider-regalo {
  position: absolute;
  cursor: pointer;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: #ccc;
  transition: 0.4s;
  border-radius: 34px;
  box-shadow: 0 0 5px #00f, 0 0 10px #0f0, 0 0 15px #ff0;
  animation: glowNeon 3s linear infinite;
}

.slider-regalo:before {
  position: absolute;
  content: "";
  height: 26px;
  width: 26px;
  left: 4px;
  bottom: 4px;
  background-color: white;
  transition: 0.4s;
  border-radius: 50%;
}

input:checked + .slider-regalo {
  background-color: #2196F3;
}

input:checked + .slider-regalo:before {
  transform: translateX(26px);
}

@keyframes glowNeon {
  0% {
    box-shadow: 0 0 5px #00f, 0 0 10px #0f0, 0 0 15px #ff0;
  }
  33% {
    box-shadow: 0 0 10px #0f0, 0 0 15px #ff0, 0 0 20px #00f;
  }
  66% {
    box-shadow: 0 0 15px #ff0, 0 0 20px #00f, 0 0 25px #0f0;
  }
  100% {
    box-shadow: 0 0 5px #00f, 0 0 10px #0f0, 0 0 15px #ff0;
  }
}