html {
  box-sizing: border-box;
  font-size: 16px;
}
*, *:before, *:after {
  box-sizing: inherit;
}

body {
  background: #f4f4f4;
  font-family: Arial, sans-serif;
  text-align: center;
  color: #222;
  margin: 0;
  min-height: 100vh;
}

/* Encabezado */
h1 {
  margin-top: 2rem;
  color: #3498db;
  font-size: clamp(1.6rem, 4vw, 2.7rem);
}

/* Tablero responsive */
#board {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(4, 1fr);
  gap: 0.7rem;
  justify-content: center;
  align-items: center;
  margin: 2.2rem auto 1.3rem auto;
  width: 100%;
  max-width: 410px;
  aspect-ratio: 1 / 1;
  background: #e9ecef;
  border-radius: 1.2rem;
  padding: 1.2rem;
  box-shadow: 0 2px 14px #bbb4;
}

/* Ficha */
.tile {
  background: #fff;
  border-radius: 0.6em;
  box-shadow: 0 2px 8px #bbb;
  font-size: clamp(1.1em, 5vw, 2em);
  font-weight: bold;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background 0.15s;
  user-select: none;
  min-width: 0; /* Para que flex funcionen perfecto en grid */
  min-height: 0;
  aspect-ratio: 1 / 1;
  /* width y height no son necesarias, grid y aspect-ratio lo ajustan */
}
.tile.empty {
  background: #bdd4ea;
  cursor: default;
  box-shadow: none;
}

/* Estado y botón */
#status {
  font-size: clamp(1em, 2vw, 1.15em);
  min-height: 2em;
  margin-bottom: 1em;
}

#restart-btn {
  background: #3498db;
  color: #fff;
  font-size: clamp(1em, 2vw, 1.15em);
  border: none;
  border-radius: 0.7em;
  padding: 0.5em 2em;
  cursor: pointer;
  transition: background 0.2s;
  margin-bottom: 1.4em;
  box-shadow: 0 2px 8px #3498db33;
}
#restart-btn:hover {
  background: #217dbb;
}

/* ==== Pantallas pequeñas/móviles ==== */
@media (max-width: 728px) {
  h1 {
    margin-top: 6vw;
    font-size: clamp(1.1em, 7vw, 2.1em);
  }
  #board {
    max-width: 96vw;
    padding: 2vw;
    gap: 3vw;
    border-radius: 6vw;
    margin-top: 6vw;
    margin-bottom: 6vw;
  }
  .tile {
    font-size: clamp(1em, 10vw, 2.6em);
    border-radius: 5vw;
  }
  #restart-btn {
    font-size: clamp(1em, 8vw, 1.5em);
    padding: 1em 13vw;
    border-radius: 5vw;
    margin-bottom: 5vw;
  }
  #status {
    font-size: clamp(1em, 7vw, 1.3em);
    margin-bottom: 4vw;
  }
}

/* ==== Pantallas muy pequeñas ==== */
@media (max-width: 350px) {
  #board {
    padding: 1vw;
    gap: 2vw;
    border-radius: 9vw;
  }
  .tile { font-size: clamp(0.9em, 15vw, 1.6em); }
  #restart-btn {
    padding: 0.7em 3vw;
    border-radius: 8vw;
    font-size: clamp(0.9em, 13vw, 1.1em);
  }
}