/* 15×15五子棋专用CSS - 修复3×75问题 */
body {
  margin: 0;
  padding: 20px;
  background-color: #f8f9fa;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  display: flex;
  justify-content: center;
  min-height: 100vh;
}

/* 棋盘容器 - 关键：使用网格布局 */
#game-board {
  width: 840px;
  height: 840px;
  margin: 0 auto;
  border: 2px solid #343a40;
  box-sizing: border-box;
  display: grid; /* ✅ 关键修复：必须设置为grid */
  grid-template-columns: repeat(15, 56px); /* 15列 */
  grid-template-rows: repeat(15, 56px);    /* 15行 */
  gap: 1px; /* 格子间距 */
}

/* 棋盘格子 */
.cell {
  box-sizing: border-box;
  border: 1px solid #343a40;
  background-color: #ffffff;
  cursor: pointer;
  user-select: none;
  transition: all 0.2s;
  font-size: 1.8rem;
  display: flex;
  align-items: center;
  justify-content: center;
}

.cell:hover {
  background-color: #e2e6ea;
  transform: scale(1.03);
}

#status {
  text-align: center;
  font-size: 1.3rem;
  font-weight: bold;
  margin: 15px 0;
  color: #2c3e50;
  min-height: 30px;
}

.mode-buttons {
  display: flex;
  justify-content: center;
  gap: 20px;
  margin: 20px 0;
}

.mode-btn {
  padding: 12px 25px;
  font-size: 1.1rem;
  background: #007bff;
  color: white;
  border: none;
  border-radius: 5px;
  cursor: pointer;
  transition: all 0.3s;
}

.mode-btn:hover {
  background: #0056b3;
  transform: translateY(-2px);
}