:root {
        --brand: #2563EB;
        --brand-hover: #1D4ED8;
        --brand-light: #EFF6FF;
        --brand-bg: #DBEAFE;
        --bg: #F8FAFC;
        --card: #FFFFFF;
        --border: #E5E7EB;
        --border-light: #F3F4F6;
        --text: #111827;
        --text-secondary: #6B7280;
        --text-muted: #9CA3AF;
        --success: #10B981;
        --success-light: #ECFDF5;
        --warning: #F59E0B;
        --warning-light: #FFFBEB;
        --error: #EF4444;
        --error-light: #FEF2F2;
        --free: #059669;
        --free-light: #ECFDF5;
        --ad: #EA580C;
        --ad-light: #FFF7ED;
        --radius-lg: 16px;
        --radius-md: 12px;
        --radius-sm: 8px;
        --radius-xs: 6px;
        --shadow-sm: 0 1px 2px rgba(0,0,0,0.04);
        --shadow-md: 0 1px 3px rgba(0,0,0,0.05), 0 1px 2px rgba(0,0,0,0.03);
        --shadow-lg: 0 4px 12px rgba(0,0,0,0.06);
        --shadow-xl: 0 8px 24px rgba(0,0,0,0.08);
    }

    * { margin: 0; padding: 0; box-sizing: border-box; }

    body {
        font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'PingFang SC', 'Microsoft YaHei', sans-serif;
        background: var(--bg);
        min-height: 100vh;
        color: var(--text);
        font-size: 13px;
        line-height: 1.5;
        -webkit-font-smoothing: antialiased;
    }

/* ===== 按钮系统 ===== */
    .btn {
        padding: 8px 16px;
        border: none;
        border-radius: var(--radius-sm);
        font-size: 13px;
        cursor: pointer;
        transition: all 0.2s;
        font-weight: 500;
        display: inline-flex;
        align-items: center;
        justify-content: center;
        gap: 6px;
    }
    .btn-primary {
        background: var(--brand);
        color: white;
    }
    .btn-primary:hover { background: var(--brand-hover); transform: translateY(-1px); box-shadow: var(--shadow-md); }
    .btn-secondary {
        background: #F3F4F6;
        color: var(--text-secondary);
        border: 1px solid var(--border);
    }
    .btn-secondary:hover { background: #E5E7EB; }
    .btn-success {
        background: var(--success);
        color: white;
    }
    .btn-success:hover { background: #059669; }
    .btn-warning {
        background: var(--warning);
        color: white;
    }
    .btn:disabled {
        background: #E5E7EB;
        color: var(--text-muted);
        cursor: not-allowed;
        transform: none;
        box-shadow: none;
    }

/* ===== 主卡片 ===== */
    .main-card {
        background: var(--card);
        border-radius: var(--radius-lg);
        padding: 32px;
        box-shadow: var(--shadow-md);
        border: 1px solid var(--border-light);
        max-width: 960px;
        margin: 0 auto;
    }