body {
  margin: 0px;
  padding: 0px;
}

main {
  width: 100%;
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
}

main .container {
  max-width: 800px;
  margin: 0 auto;
  padding: 20px;
  display: grid;
  grid-template-columns: 1fr;
  row-gap: 10px;
}

main .container .title {
  text-align: center;
  font-size: 36px;
  font-family: 'Montserrat', sans-serif;
}

main .container .puzzle-board {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(4, 1fr);
  grid-gap: 10px;
  background-color: #fff;
  border: 2px solid #333;
  padding: 10px;
}

main .container .puzzle-board .puzzle-tile {
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 48px;
  font-weight: bold;
  color: #333;
  background-color: #eee;
  border: 2px solid #333;
  cursor: pointer;
  transition: all 0.3s ease;
  user-select: none;
}

main .container .puzzle-board .puzzle-tile:hover {
  background-color: #ccc;
}

main .container .puzzle-board .puzzle-tile.dragging {
  opacity: 0.5;
}

main .container .puzzle-board .puzzle-tile.empty-tile {
  background-color: gray;
  color: #fff;
  border: none;
  cursor: default;
}

main .container .buttons {
  display: flex;
  justify-content: center;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
  user-select: none;
}

main .container button {
  display: block;
  margin: 0 auto;
  padding: 10px 12px;
  font-size: 16px;
  font-weight: bold;
  color: #fff;
  background-color: rgba(70, 131, 180, 0.7);
  border: none;
  border-radius: 3px;
  cursor: pointer;
  transition: all 0.3s ease;
  user-select: none;
}

main .container button.easyBtn {
  background-color: rgba(0, 128, 0, 0.7);
}

main .container button.easyBtn:hover {
  background-color: rgba(0, 128, 0, 0.8);
}

main .container button.mediumBtn {
  background-color: rgba(255, 166, 0, 0.7);
}

main .container button.mediumBtn:hover {
  background-color: rgba(255, 166, 0, 0.8);
}

main .container button.hardBtn {
  background-color: rgba(255, 0, 0, 0.7);
}

main .container button.hardBtn:hover {
  background-color: rgba(255, 0, 0, 0.8);
}

main .container button:hover {
  background-color: rgba(70, 131, 180, 0.8);
  box-shadow: rgba(0, 0, 0, 0.35) 0px 2px 5px;
}

@media screen and (max-width: 400px) {
  main .container .puzzle-board .puzzle-tile {
    font-size: 32px;
  }
}

@media screen and (max-width: 380px) {
  main .container .puzzle-board .puzzle-tile {
    font-size: 30px;
  }
}