:root {
    /* 响应式格子大小：尽可能填满屏幕宽度，最大不超过 50px (移动端) */
    /* 计算逻辑：(100vw - 容器内边距 - 页面内边距 - 间隙) / 9 */
    /* 假设 padding 约 40px，gap 8px -> 48px */
    --cell-size: min(54px, calc((100vw - 40px) / 9));
    --wall-thickness: 10px; /* 移动端稍厚一点更易点击 */
    --gap-size: 0px; 
    
    /* 现代调色板 */
    --board-bg: #e2e8f0; /* 柔和的 slate-200 用于网格线 */
    --cell-bg: #ffffff;
    --cell-hover: #f8fafc; /* 非常微妙的悬停效果 */
    
    --wall-color: #334155; /* slate-700 颜色 */
    --wall-hover: rgba(51, 65, 85, 0.3);
    
    /* 玩家颜色 - 鲜艳但哑光 */
    --p1-color: #3b82f6; /* 蓝色-500 */
    --p2-color: #ef4444; /* 红色-500 */
    --p3-color: #10b981; /* 翡翠色-500 */
    --p4-color: #f59e0b; /* 琥珀色-500 */
    
    --shadow-soft: 0 4px 6px -1px rgba(0, 0, 0, 0.05), 0 2px 4px -1px rgba(0, 0, 0, 0.03);
    --shadow-float: 0 10px 15px -3px rgba(0, 0, 0, 0.08), 0 4px 6px -2px rgba(0, 0, 0, 0.04);
}

@media (min-width: 640px) {
    :root {
        --cell-size: 54px; /* 更大 */
        --wall-thickness: 12px;
    }
}

.board-container {
    display: inline-block;
    background: var(--board-bg);
    padding: 1px; /* 最小边框 */
    border-radius: 8px; /* 圆角 */
    user-select: none;
    box-shadow: var(--shadow-float);
    max-width: 100%;
}

/* 增加触摸热区大小，提升移动端体验 */
.wall-hotspot {
    touch-action: none; 
}

#board {
    display: grid;
    grid-template-columns: repeat(9, var(--cell-size));
    grid-template-rows: repeat(9, var(--cell-size));
    gap: 1px; 
    background-color: var(--board-bg);
    border-radius: 7px; /* 内圆角 */
    overflow: hidden; /* 裁剪格子以适应圆角 */
}

/* 棋盘格子 */
.cell {
    width: var(--cell-size);
    height: var(--cell-size);
    background-color: var(--cell-bg);
    border: none;
    border-radius: 0;
    position: relative;
    cursor: pointer;
    transition: background-color 0.15s ease;
}

.cell:hover {
    background-color: var(--cell-hover);
    z-index: 1;
}

/* 玩家棋子 - 极简主义 */
.pawn {
    width: 50%; /* 更小以显优雅 */
    height: 50%;
    border-radius: 50%;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    z-index: 10;
    transition: all 0.4s cubic-bezier(0.2, 0.8, 0.2, 1); /* 平滑弹簧动画 */
    pointer-events: none;
    
    /* 文字居中 */
    display: flex;
    justify-content: center;
    align-items: center;
    color: white;
    font-weight: 600;
    font-size: 1rem;
    
    /* 哑光质感，无强烈阴影 */
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.pawn.p1 { background: var(--p1-color); }
.pawn.p2 { background: var(--p2-color); }
.pawn.p3 { background: var(--p3-color); }
.pawn.p4 { background: var(--p4-color); }

/* 可移动提示 - 微妙圆点 */
.cell.valid-move::after {
    content: '';
    position: absolute;
    width: 8px;
    height: 8px;
    background: #cbd5e1; /* slate-300 颜色 */
    border-radius: 50%;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    transition: all 0.2s;
    opacity: 0.6;
}

.cell.valid-move:hover::after {
    background: #94a3b8; /* slate-400 颜色 */
    transform: translate(-50%, -50%) scale(1.4);
    opacity: 1;
}

/* 墙的容器层 */
#wall-layer {
    z-index: 20;
}

/* 墙 - 现代扁平风格 */
.wall {
    position: absolute;
    background-color: var(--wall-color);
    border-radius: 99px; /* 胶囊形状 */
    z-index: 5;
    box-shadow: 0 2px 4px rgba(0,0,0,0.15); /* 柔和抬起效果 */
    pointer-events: auto; 
    transition: opacity 0.2s, background-color 0.2s, transform 0.2s;
}

/* 墙的样式：水平 */
.wall.h {
    height: var(--wall-thickness);
    width: calc(2 * var(--cell-size) + 1px);
}

/* 墙的样式：垂直 */
.wall.v {
    width: var(--wall-thickness);
    height: calc(2 * var(--cell-size) + 1px);
}

/* 预览墙 */
.wall.preview {
    opacity: 0.4;
    cursor: pointer;
    background-color: var(--wall-color);
    box-shadow: none;
    transform: scale(0.95); /* 稍小以指示预览 */
}

.wall.preview.invalid {
    background-color: #ef4444 !important; 
    opacity: 0.2;
    cursor: not-allowed;
}

/* 活跃玩家状态 */
.player-status {
    border: 2px solid transparent;
    transition: all 0.3s;
    background: white;
}
.player-status.active {
    background-color: #f8fafc;
    border-color: #e2e8f0;
    transform: translateY(-2px);
    box-shadow: 0 10px 15px -3px rgba(0, 0, 0, 0.05);
}

.player-status.p1-active {
    border-color: var(--p1-color);
}
.player-status.p2-active {
    border-color: var(--p2-color);
}
.player-status.p3-active {
    border-color: var(--p3-color);
}
.player-status.p4-active {
    border-color: var(--p4-color);
}

/* 模态框 */
.modal-overlay {
    position: fixed;
    top: 0; left: 0; right: 0; bottom: 0;
    background: rgba(15, 23, 42, 0.5); /* slate-900/50 颜色 */
    backdrop-filter: blur(4px);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 1000;
}

.modal-overlay.hidden {
    display: none;
}

.modal {
    background: white;
    border-radius: 16px;
    padding: 32px;
    width: 90%;
    max-width: 400px;
    box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    text-align: center;
    animation: modal-pop 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}

@keyframes modal-pop {
    0% { transform: scale(0.8); opacity: 0; }
    100% { transform: scale(1); opacity: 1; }
}

.modal-header h2 {
    margin-bottom: 24px;
}

.winner-display {
    display: flex;
    flex-direction: column;
    align-items: center;
    margin-bottom: 24px;
}

.winner-icon {
    margin-bottom: 16px;
}

.winner-title {
    font-size: 1.5rem;
    font-weight: 800;
    color: #1e293b;
}

.modal-footer {
    display: flex;
}

.btn.primary {
    width: 100%;
    padding: 12px;
    font-size: 1.1rem;
    background: linear-gradient(to right, #0ea5e9, #0284c7); /* 天蓝色渐变 */
    color: white;
    border: none;
    border-radius: 12px;
    font-weight: bold;
    cursor: pointer;
    box-shadow: 0 4px 6px -1px rgba(14, 165, 233, 0.3);
    transition: all 0.2s;
}

.btn.primary:hover {
    transform: translateY(-1px);
    box-shadow: 0 6px 8px -1px rgba(14, 165, 233, 0.4);
}

.btn.secondary {
    background: white;
    color: #64748b;
    border: 1px solid #cbd5e1;
    padding: 12px;
    border-radius: 12px;
    font-weight: bold;
    cursor: pointer;
    transition: all 0.2s;
}

.btn.secondary:hover {
    background: #f1f5f9;
    color: #334155;
    border-color: #94a3b8;
}

/* 响应式调整 */
@media (max-width: 480px) {
    :root {
        --cell-size: 32px;
        --gap-size: 10px;
    }
    .board-container {
        padding: 16px;
    }
}