:root {
            --primary: #0066FF;
            --primary-soft: #F0F7FF;
            --text-main: #1D2129;
            --text-sub: #4E5969;
            --bg-page: #F4F7F9;
            --border-color: #E5E6EB;
            --accent-orange: #FF9500;
            --max-width: 1050px;
        }

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

        body {
            background-color: var(--bg-page);
            font-family: -apple-system, system-ui, "PingFang SC", "Microsoft YaHei", sans-serif;
            color: var(--text-main);
            line-height: 1.8;
            -webkit-font-smoothing: antialiased;
            padding-top: 80px;
        }

        /* 顶部导航 */
        nav {
            position: fixed;
            top: 0;
            width: 100%;
            height: 72px;
            background: rgba(255, 255, 255, 0.9);
            backdrop-filter: blur(15px);
            border-bottom: 1px solid var(--border-color);
            z-index: 1000;
            display: flex;
            justify-content: center;
        }

        .nav-inner {
            width: var(--max-width);
            display: flex;
            align-items: center;
            justify-content: space-between;
            padding: 0 24px;
        }

        .logo { font-size: 22px; font-weight: 800; color: var(--primary); letter-spacing: -0.5px; }

        /* 内容容器 */
        .container {
            max-width: var(--max-width);
            margin: 0 auto;
            padding: 20px 24px 100px;
        }

        .main-header { margin-bottom: 40px; text-align: left; }
        .main-header h1 { font-size: 36px; font-weight: 900; color: var(--text-main); margin-bottom: 20px; }

        /* 学习目标 */
        .goal-card {
            background: #fff;
            border-radius: 16px;
            padding: 24px 32px;
            border: 1px solid var(--border-color);
            display: flex;
            flex-wrap: wrap;
            gap: 20px 40px;
            margin-bottom: 40px;
        }

        .goal-item { display: flex; align-items: center; font-size: 16px; font-weight: 600; color: var(--text-sub); }
        .goal-item::before { content: "✓"; margin-right: 8px; color: var(--primary); font-weight: 900; }

        /* 任务卡片通用风格 (1-5) */
        .task-card {
            background: #fff;
            border-radius: 20px;
            margin-bottom: 32px;
            padding: 48px;
            border: 1px solid var(--border-color);
            position: relative;
            transition: transform 0.2s ease;
        }

        .task-card::before {
            content: "";
            position: absolute;
            top: 0;
            left: 0;
            width: 6px;
            height: 100%;
            background: var(--primary);
            border-radius: 20px 0 0 20px;
        }

        .task-label {
            font-size: 14px;
            font-weight: 800;
            color: var(--primary);
            text-transform: uppercase;
            letter-spacing: 2px;
            margin-bottom: 12px;
            display: block;
        }

        .task-title {
            font-size: 30px; /* 加大字号 */
            font-weight: 800;
            color: var(--text-main);
            margin-bottom: 40px;
        }

        /* 题目样式 */
        .q-item { margin-bottom: 40px; }
        .q-item:last-child { margin-bottom: 0; }

        .q-text {
            font-size: 20px;
            font-weight: 700;
            color: var(--text-main);
            margin-bottom: 16px;
            display: flex;
            gap: 12px;
        }

        .q-num { color: var(--primary); opacity: 0.4; font-style: italic; font-family: Georgia, serif; }

        /* 提示块 */
        .note-box {
            background: #FFF9F2;
            border-left: 4px solid var(--accent-orange);
            padding: 24px;
            margin: 16px 0 20px 32px;
            border-radius: 0 8px 8px 0;
            font-size: 17px;
        }

        .info-box {
            background: var(--primary-soft);
            border-left: 4px solid var(--primary);
            padding: 24px;
            margin: 16px 0 20px 32px;
            border-radius: 0 8px 8px 0;
            font-size: 17px;
        }

        /* 答案系统 */
        .ans-btn {
            background: #fff;
            border: 1px solid var(--border-color);
            padding: 10px 24px;
            border-radius: 10px;
            font-size: 15px;
            font-weight: 600;
            color: var(--text-sub);
            cursor: pointer;
            margin-left: 32px;
            transition: all 0.2s;
        }

        .ans-btn:hover { border-color: var(--primary); color: var(--primary); }

        .ans-panel {
            display: none;
            margin: 20px 0 0 32px;
            padding: 30px;
            background: #F9FAFB;
            border-radius: 16px;
            border: 1px dashed var(--border-color);
            font-size: 17px;
            animation: slideDown 0.3s ease-out;
        }

        .ans-panel.active { display: block; }

        @keyframes slideDown { from { opacity: 0; transform: translateY(-10px); } to { opacity: 1; transform: translateY(0); } }

        img { max-width: 100%; border-radius: 12px; margin-top: 20px; border: 1px solid var(--border-color); }

        footer { text-align: center; padding: 40px; color: #999; font-size: 14px; }

        @media (max-width: 768px) {
            .task-card { padding: 30px; }
            .note-box, .info-box, .ans-btn, .ans-panel { margin-left: 0; }
        }