body {
  width: 90%;
  max-width: 450px;

  background-color: lightgray;
  
  font-family: 'Courier New', Courier, monospace;
  margin: auto;
}

.info{
  display: flex;
  justify-content: center;
  padding-top: 15px;
  padding-bottom: 10px;

  width: 100%;

  font-size: 1.2em;
  text-align: center;
}

.gameboard{
  display: grid;
  grid-template-columns: 25% 25% 25% 25%;
  grid-template-rows: 25% 25% 25% 25%;

  height: 90vw;
  max-height: 450px;

  margin: 0;
  padding: 0;
}

.card {
  width:100%;
  cursor: pointer;
}

.guessed {
  opacity: 0.3;
}

.control {
  padding-top: 5px;

  width:100%;

  font-size: 10px;
  text-align: center;
  transition-duration: 0.5s;
}

.hide {
  display: none;
}

.start-btn {
  margin-top: 10px;
  padding: 10px;

  border: none;
  border-radius: 10px;

  font-weight: bold;
  background-color: gray;
  color: white;
  box-shadow: 3px 6px #555555;
  cursor: pointer;
}

.start-btn:hover {
  background-color: darkgreen;
}

.start-btn:active {
  background-color: yellowgreen;
  box-shadow: 3px 3px #555555;
  transform: translateY(3px);
}

.preview-option {
  cursor: pointer;
}

.flip-container {
  perspective: 1000px;

}

.opened .flipper {
  transform: rotateY(180deg);
}

.flip-container, .front, .back {
  width: 100%;
  height: 100%;
}

.flipper {
  position: relative;
  
	transition: 0.3s;
	transform-style: preserve-3d;
}

.front, .back {
  position: absolute;
  top: 0;
  left: 0;
  
  -webkit-backface-visibility: hidden;
  backface-visibility: hidden;
}

.front {
	z-index: 2;
	transform: rotateY(0deg);
}

.back {
	transform: rotateY(180deg);
}