:root {
    --primary: #059669; /* 学术绿 */
    --primary-hover: #047857;
    --accent: #fbbf24; /* 护眼黄 */
    --bg-main: #f8fafc; /* 纸张白 */
    --bg-card: #ffffff;
    --text-dark: #1e293b;
    --text-muted: #64748b;
    --border: #e2e8f0;
    --shadow-soft: 0 4px 6px -1px rgba(0,0,0,0.05), 0 2px 4px -1px rgba(0,0,0,0.03);
    --shadow-hover: 0 10px 15px -3px rgba(0,0,0,0.1), 0 4px 6px -2px rgba(0,0,0,0.05);
}

* { margin: 0; padding: 0; box-sizing: border-box; }
body { 
    font-family: "PingFang SC", "Microsoft YaHei", -apple-system, sans-serif;
    background-color: var(--bg-main); color: var(--text-dark); line-height: 1.7;
    /* 轻微护眼纸张纹理感 */
    background-image: radial-gradient(#e2e8f0 1px, transparent 1px); background-size: 24px 24px;
}
a { text-decoration: none; color: inherit; transition: 0.3s; }
ul { list-style: none; }
img { max-width: 100%; display: block; border-radius: 12px; }

.container { max-width: 1100px; margin: 0 auto; padding: 0 24px; }

/* 导航 */
header { 
    background: rgba(255,255,255,0.95); backdrop-filter: blur(8px);
    border-bottom: 2px solid var(--primary); position: sticky; top: 0; z-index: 100;
}
.nav-inner { display: flex; justify-content: space-between; align-items: center; height: 70px; }
.logo-area { display: flex; align-items: center; gap: 10px; }
.logo { font-size: 24px; font-weight: 800; color: var(--primary); letter-spacing: 1px; }
.logo-tag { background: #dcfce7; color: var(--primary); font-size: 12px; padding: 3px 8px; border-radius: 12px; font-weight: bold; border: 1px solid #bbf7d0; }
.nav-links { display: flex; gap: 32px; }
.nav-links a { font-size: 15px; font-weight: 600; color: var(--text-muted); }
.nav-links a:hover, .nav-links a.active { color: var(--primary); }

/* 按钮 */
.btn {
    display: inline-flex; align-items: center; justify-content: center;
    padding: 12px 32px; border-radius: 30px; font-weight: 700; font-size: 16px;
    cursor: pointer; border: none; transition: 0.3s;
}
.btn-primary { background: var(--primary); color: #fff; box-shadow: 0 4px 10px rgba(5,150,105,0.3); }
.btn-primary:hover { background: var(--primary-hover); transform: translateY(-2px); box-shadow: 0 6px 15px rgba(5,150,105,0.4); }
.btn-outline { background: #fff; color: var(--primary); border: 2px solid var(--primary); }
.btn-outline:hover { background: #ecfdf5; }

/* Hero区 */
.hero { padding: 80px 0 100px; text-align: center; position: relative; }
.hero-content { background: var(--bg-card); border-radius: 24px; padding: 60px 40px; box-shadow: var(--shadow-soft); border: 1px solid var(--border); }
.hero h1 { font-size: 48px; font-weight: 900; color: var(--text-dark); margin-bottom: 20px; }
.hero h1 span { position: relative; z-index: 1; }
.hero h1 span::after { content: ''; position: absolute; bottom: 8px; left: 0; width: 100%; height: 12px; background: var(--accent); opacity: 0.4; z-index: -1; transform: rotate(-1deg); }
.hero p { font-size: 18px; color: var(--text-muted); margin-bottom: 40px; max-width: 600px; margin-left: auto; margin-right: auto; line-height: 1.8; }
.hero-btns { display: flex; justify-content: center; gap: 20px; margin-bottom: 50px; }
.hero-img-box { border-radius: 16px; overflow: hidden; border: 4px solid #f1f5f9; box-shadow: var(--shadow-hover); position: relative; }
.hero-img-box::before { content: '✎ 沉浸式网页阅读'; position: absolute; top: 15px; left: -10px; background: var(--accent); color: #000; font-weight: bold; font-size: 14px; padding: 4px 15px; border-radius: 4px; box-shadow: 2px 2px 5px rgba(0,0,0,0.2); z-index: 2; }

/* 模块通用 */
section { padding: 80px 0; }
.sec-title { text-align: center; font-size: 32px; font-weight: 800; margin-bottom: 50px; color: var(--text-dark); }
.sec-title::after { content: ''; display: block; width: 60px; height: 4px; background: var(--primary); margin: 15px auto 0; border-radius: 2px; }

/* 核心卖点 - 学习卡片 */
.grid-features { display: grid; grid-template-columns: repeat(5, 1fr); gap: 20px; }
.f-card { background: var(--bg-card); padding: 30px 20px; border-radius: 16px; text-align: center; box-shadow: var(--shadow-soft); transition: 0.3s; border: 1px solid var(--border); }
.f-card:hover { transform: translateY(-5px); box-shadow: var(--shadow-hover); border-color: var(--primary); }
.f-card img { width: 50px; height: 50px; margin: 0 auto 15px; background: #ecfdf5; padding: 10px; border-radius: 50%; }
.f-card h3 { font-size: 16px; font-weight: 700; margin-bottom: 8px; color: var(--text-dark); }
.f-card p { font-size: 13px; color: var(--text-muted); }

/* 功能详情 - 笔记风格 */
.detail-item { display: flex; align-items: center; gap: 50px; margin-bottom: 60px; background: var(--bg-card); padding: 40px; border-radius: 24px; box-shadow: var(--shadow-soft); border: 1px solid var(--border); }
.detail-item:nth-child(even) { flex-direction: row-reverse; }
.d-text { flex: 1; }
.d-text h3 { font-size: 26px; font-weight: 800; margin-bottom: 20px; color: var(--primary); display: flex; align-items: center; gap: 10px; }
.d-text h3::before { content: '📚'; font-size: 24px; }
.d-text p { font-size: 16px; color: var(--text-muted); margin-bottom: 20px; }
.d-tag { display: inline-block; background: #fffbeb; color: #b45309; padding: 6px 12px; border-radius: 8px; font-size: 14px; font-weight: bold; border: 1px dashed #fcd34d; }
.d-img { flex: 1; border: 8px solid #f8fafc; border-radius: 16px; box-shadow: 0 4px 10px rgba(0,0,0,0.05); }

/* 对比表格 - 黑板/白板风 */
.compare-box { background: var(--bg-card); border-radius: 16px; padding: 40px; box-shadow: var(--shadow-soft); border: 1px solid var(--border); }
.compare-tb { width: 100%; border-collapse: collapse; text-align: center; }
.compare-tb th, .compare-tb td { padding: 18px; border-bottom: 1px dashed var(--border); }
.compare-tb th { color: var(--text-muted); font-weight: 600; font-size: 15px; background: #f8fafc; }
.compare-tb .hl { color: var(--primary); font-weight: 800; font-size: 16px; background: #ecfdf5; border-radius: 8px; }

/* 下载版本 */
.v-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 30px; }
.v-card { background: var(--bg-card); border: 1px solid var(--border); padding: 40px 30px; border-radius: 20px; text-align: center; transition: 0.3s; position: relative; }
.v-card:hover { transform: translateY(-8px); box-shadow: var(--shadow-hover); border-color: var(--primary); }
.v-card.rec { border: 2px solid var(--primary); background: #f0fdf4; }
.v-card.rec::after { content: '⭐ 学生推荐'; position: absolute; top: -15px; left: 50%; transform: translateX(-50%); background: var(--accent); color: #000; padding: 5px 16px; border-radius: 20px; font-size: 13px; font-weight: 800; box-shadow: 0 4px 6px rgba(0,0,0,0.1); }
.v-card h3 { font-size: 24px; font-weight: 800; margin-bottom: 15px; color: var(--text-dark); }
.v-card p { font-size: 14px; color: var(--text-muted); margin-bottom: 30px; height: 45px; }

/* 数据背书 */
.data-sec { background: var(--primary); color: #fff; padding: 60px 0; border-radius: 24px; margin: 40px 24px; }
.data-wrap { display: flex; justify-content: space-around; flex-wrap: wrap; text-align: center; gap: 30px; }
.data-item h4 { font-size: 48px; font-weight: 900; margin-bottom: 5px; text-shadow: 0 2px 4px rgba(0,0,0,0.2); }
.data-item p { font-size: 16px; font-weight: 600; opacity: 0.9; }

/* FAQ */
.faq-wrap { column-count: 2; column-gap: 30px; }
.faq-box { background: var(--bg-card); padding: 20px; border-radius: 12px; border: 1px solid var(--border); margin-bottom: 20px; break-inside: avoid; border-left: 4px solid var(--accent); box-shadow: var(--shadow-soft); }
.faq-box h4 { font-size: 15px; font-weight: 700; color: var(--text-dark); margin-bottom: 10px; }
.faq-box p { font-size: 14px; color: var(--text-muted); }

footer { text-align: center; padding: 40px 0; color: var(--text-muted); font-size: 14px; border-top: 1px solid var(--border); }