start_btn.onclick = () => {
  info_box.classList.add("activeInfo");
};

.btn-12 {
  align-items: center;
  position: relative;
  right: 30%;
  bottom: 200px;
  border: none;
  box-shadow: none;
  line-height: 42px;
  -webkit-perspective: 230px;
  perspective: 230px;
}

.btn-12 span {
  background: rgb(0, 172, 238);
  background: linear-gradient(0deg, rgba(0, 172, 238, 1) 0%, rgba(2, 126, 251, 1) 100%);
  display: block;
  position: absolute;
  width: 250px;
  height: 40px;
  box-shadow: inset 2px 2px 2px 0px rgba(255, 255, 255, .5), 7px 7px 20px 0px rgba(0, 0, 0, .1), 4px 4px 5px 0px rgba(0, 0, 0, .1);
  border-radius: 5px;
  margin: 0;
  text-align: center;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
  -webkit-transition: all .3s;
  transition: all .3s;
}

.btn-12 span:nth-child(1) {
  box-shadow: -7px -7px 20px 0px #fff9, -4px -4px 5px 0px #fff9, 7px 7px 20px 0px #0002, 4px 4px 5px 0px #0001;
  -webkit-transform: rotateX(90deg);
  -moz-transform: rotateX(90deg);
  transform: rotateX(90deg);
  -webkit-transform-origin: 50% 50% -20px;
  -moz-transform-origin: 50% 50% -20px;
  transform-origin: 50% 50% -20px;
}

.btn-12 span:nth-child(2) {
  -webkit-transform: rotateX(0deg);
  -moz-transform: rotateX(0deg);
  transform: rotateX(0deg);
  -webkit-transform-origin: 50% 50% -20px;
  -moz-transform-origin: 50% 50% -20px;
  transform-origin: 50% 50% -20px;
}

.btn-12:hover span:nth-child(1) {
  box-shadow: inset 2px 2px 2px 0px rgba(255, 255, 255, .5), 7px 7px 20px 0px rgba(0, 0, 0, .1), 4px 4px 5px 0px rgba(0, 0, 0, .1);
  -webkit-transform: rotateX(0deg);
  -moz-transform: rotateX(0deg);
  transform: rotateX(0deg);
}

.btn-12:hover span:nth-child(2) {
  box-shadow: inset 2px 2px 2px 0px rgba(255, 255, 255, .5), 7px 7px 20px 0px rgba(0, 0, 0, .1), 4px 4px 5px 0px rgba(0, 0, 0, .1);
  color: transparent;
  -webkit-transform: rotateX(-90deg);
  -moz-transform: rotateX(-90deg);
  transform: rotateX(-90deg);
}

<div id="start_btn">
  <button ><span>ｲ