styles.css

:root {
  --primary-color: #4caf50;
  --primary-hover: #45a049;
  --primary-active: #3e8e41;
  --background-color: #f0f0f0;
  --card-background: #ddd;
  --card-flipped: #fff;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: 'Lucida Sans', 'Lucida Sans Regular', Geneva, Verdana, sans-serif;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background-color: var(--background-color);
}

.container {
  text-align: center;
  max-width: 37.5rem;
  margin: 0 auto;
  padding: 1.25rem;
}

h1.title {
  margin-bottom: 1.25rem;
}

.game-info {
  display: flex;
  margin-bottom: 1.25rem;
  gap: 0.8rem;
}

.game-info span {
  /* display: grid;
  grid-template-columns: repeat(4, 1fr); */
  flex: 1;
  text-align: center;
}

.start-stop-btn {
  background-color: var(--primary-color);
  border: none;
  color: white;
  padding: 1rem 2rem;
  text-align: center;
  text-decoration: none;
  display: inline-flex;
  font-size: 1rem;
  margin: 1rem 0.0625rem;
  cursor: pointer;
  border-radius: 0.5rem;
  transition: background-color 0.3s ease;
}

.start-stop-btn:hover {
  background-color: var(--primary-hover);
}

.start-stop-btn:active {
  background-color: var(--primary-active);
}

.game-board {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.625rem;
  max-width: 37.5rem;
  margin: 0 auto;
  animation: fadeIn 0.5s ease-in-out;
}

.card {
  aspect-ratio: 3/4;
  background-color: var(--card-background);
  display: flex;
  justify-content: center;
  align-items: center;
  /* font-size: 0; */
  cursor: pointer;
  transition: transform 0.3s, background-color 0.3s;
  border-radius: 0.3rem;
}

.card.flipped {
  transform: rotateY(180deg);
  background-color: var(--card-flipped);
  font-size: 2rem;
}

.hidden {
  display: none;
}

.game-board.fade-out {
  animation: fadeOut 0.5s ease-in-out;
}

@media (max-width: 37.5rem) {
  .game-board {
    grid-template-columns: repeat(3, 1fr);
  }
}

@keyframes fadeIn {
  from {
    opacity: 0;
  }
  to {
    opacity: 1;
  }
}

@keyframes fadeOut {
  from {
    opacity: 1;
  }
  to {
    opacity: 0;
  }
}