function flipcard_main() {
  var cardFront = document.getElementsByClassName("fc-thefront");
  var i;
  var flip;
  for (i = 0; i < cardFront.length; i++) {
    flip = document.createElement("div");
    flip.appendChild(document.createTextNode("flip"));
    flip.className = "fc-flip";
    flip.addEventListener("mouseover", event => {
      var flip = event.target;
      var front = flip.parentElement;
      var card = front.parentElement;
      card.style.transform = "rotateY(180deg)";
    });
    cardFront[i].appendChild(flip);
  };

  var cardBack = document.getElementsByClassName("fc-theback");
  var i;
  for (i = 0; i < cardBack.length; i++) {
    cardBack[i].addEventListener("mouseleave", flipcard_mouseLeave, true);
  }
};
function flipcard_mouseLeave(event) {
  if (event.target.className == "fc-theback") {
    var back = event.target;
    var card = back.parentElement;
    card.style.transform = "rotateY(0deg)";
  }
};
flipcard_main();