body {
  font-family: sans-serif;
  margin: 0;
  padding: 0;
  text-align: center;
  background: #fafafa;
}
h1, h2 {
  color: #333;
}
input {
  padding: 10px;
  font-size: 16px;
  margin: 5px;
}
button {
  padding: 10px 20px;
  font-size: 16px;
  background: #4CAF50;
  color: white;
  border: none;
  border-radius: 8px;
}
button:hover {
  background: #45a049;
}
.hidden {
  display: none;
}
.board {
  display: grid;
  grid-template-columns: repeat(10, 30px);
  gap: 2px;
  justify-content: center;
  margin: 20px auto;
}
.cell {
  width: 30px;
  height: 30px;
  background: #eee;
  border-radius: 4px;
  position: relative;
}
.piece {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  margin: auto;
  position: absolute;
  top: 3px;
  left: 3px;
}
.red { background: red; }
.blue { background: blue; }
.green { background: green; }
.yellow { background: gold; }

@media (max-width: 600px) {
  .board {
    grid-template-columns: repeat(8, 24px);
    gap: 1px;
  }
  .cell {
    width: 24px;
    height: 24px;
  }
  .piece {
    width: 20px;
    height: 20px;
    top: 2px;
    left: 2px;
  }
}