#memory-game {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  max-width: 500px;
  width: 100%;
  column-gap: 3rem;
  row-gap: 3rem;
  padding: 3rem;
  margin: 0 auto 3rem;
  position: relative;
  z-index: 0;
  justify-content: center;
}

.memory-card {
  height: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 24px;
  cursor: pointer;
  box-sizing: border-box;
  transition: transform 0.8s;
  transform-style: preserve-3d;
}

.memory-card.matched,
.memory-card.open {
  transform: rotateY(180deg);
}

.memory-card.matched .memory-card-back,
.memory-card.open .memory-card-back {
  transform: rotateY(-180deg);
  display: none;
}

.memory-card.matched .memory-card-front,
.memory-card.open .memory-card-front {
  transform: rotateY(180deg);
  display: block;
}

.memory-card .memory-card-front {
  display: none;
  -webkit-backface-visibility: hidden;
  backface-visibility: hidden;
}

.memory-card .memory-card-back {
  display: block;
  -webkit-backface-visibility: hidden;
  backface-visibility: hidden;
}

.start-button-overlay {
  position: absolute;
  z-index: 1;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  display: block;
  text-align: center;
}

.start-button {
  position: absolute;
  z-index: 2;
  width: 100px;
  height: 100px;
  display: block;
  text-align: center;
  background-color: #772309;
  font-weight: 700;
  opacity: .8;
  border-radius: 50%;
  line-height: 100px;
  text-transform: uppercase;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
}

.start-button:hover {
  cursor: pointer;
}

.success-message {
  display: none;
  position: absolute;
  color: #772309;
  top: 50%;
  left: 50%;
  z-index: 3;
  transform: translate(-50%, -50%);
  font-weight: 800;
  font-family: "brotherbold", sans-serif;
  font-size: 16rem;
  width: 100%;
}