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

:root {
  --blue-primary: #3370ff;
  --blue-hover: #2860e0;
  --text-primary: #1a1a1a;
  --text-secondary: #666;
  --text-light: #999;
  --bg-page: #f5f5f5;
  --bg-white: #fff;
  --bg-nav: rgba(255, 255, 255, 0.92);
  --border-color: #e8e8e8;
  --radius-lg: 20px;
  --radius-md: 12px;
  --radius-sm: 8px;
  --shadow-nav: 0 2px 12px rgba(0, 0, 0, 0.08);
  --shadow-card: 0 4px 24px rgba(0, 0, 0, 0.06);
  --font-family: -apple-system, BlinkMacSystemFont, "SF Pro Display", "Helvetica Neue", "PingFang SC", "Microsoft YaHei", sans-serif;
  --cdn: https://lf-flow-web-cdn.doubao.com/obj/flow-doubao/doubao/desktop_online_web/static/image;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
}

body {
  font-family: var(--font-family);
  color: var(--text-primary);
  background: var(--bg-page);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

/* ========== NAV ========== */
.nav-wrapper {
  position: fixed;
  top: 16px;
  left: 50%;
  transform: translateX(-50%);
  z-index: 1000;
  width: auto;
}

.nav {
  display: flex;
  align-items: center;
  gap: 8px;
  background: var(--bg-nav);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-radius: 50px;
  padding: 8px 8px 8px 16px;
  box-shadow: var(--shadow-nav);
  border: 1px solid rgba(0, 0, 0, 0.04);
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: 8px;
  text-decoration: none;
  margin-right: 8px;
  flex-shrink: 0;
}

.nav-logo img {
  width: 32px;
  height: 32px;
  border-radius: 50%;
  object-fit: cover;
}

.nav-logo span {
  font-size: 18px;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 4px;
  list-style: none;
}

.nav-links a {
  display: block;
  padding: 6px 14px;
  font-size: 14px;
  color: var(--text-secondary);
  text-decoration: none;
  border-radius: 20px;
  transition: all 0.2s ease;
  white-space: nowrap;
}

.nav-links a:hover {
  color: var(--text-primary);
  background: rgba(0, 0, 0, 0.04);
}

.nav-links a.active {
  color: var(--text-primary);
  font-weight: 600;
}

.nav-download {
  display: inline-flex;
  align-items: center;
  padding: 8px 20px;
  background: var(--blue-primary);
  color: #fff;
  border-radius: 50px;
  font-size: 14px;
  font-weight: 500;
  text-decoration: none;
  transition: background 0.2s ease;
  white-space: nowrap;
  margin-left: 4px;
}

.nav-download:hover {
  background: var(--blue-hover);
}

/* ========== HERO ========== */
.hero {
  text-align: center;
  padding: 140px 20px 40px;
  background: var(--bg-page);
}

.hero h1 {
  font-size: 48px;
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.2;
  margin-bottom: 16px;
  color: var(--text-primary);
}

.hero-subtitle {
  font-size: 17px;
  color: var(--text-secondary);
  max-width: 600px;
  margin: 0 auto 36px;
  line-height: 1.7;
}

.cta-desc {
  font-size: 15px;
  color: var(--text-secondary);
  margin-bottom: 28px;
}

.btn-download {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 14px 40px;
  background: var(--blue-primary);
  color: #fff;
  border: none;
  border-radius: 50px;
  font-size: 18px;
  font-weight: 500;
  cursor: pointer;
  text-decoration: none;
  transition: all 0.25s ease;
  box-shadow: 0 4px 16px rgba(51, 112, 255, 0.3);
}

.btn-download:hover {
  background: var(--blue-hover);
  transform: translateY(-1px);
  box-shadow: 0 6px 24px rgba(51, 112, 255, 0.4);
}

.btn-download .apple-icon,
.btn-download .win-icon {
  width: 20px;
  height: 20px;
}

.hero-web-link {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 4px;
  margin-top: 20px;
  font-size: 15px;
  color: var(--text-secondary);
  text-decoration: none;
  transition: color 0.2s;
}

.hero-web-link:hover {
  color: var(--text-primary);
}

.hero-web-link .arrow {
  transition: transform 0.2s;
}

.hero-web-link:hover .arrow {
  transform: translateX(3px);
}

/* ========== APP MOCKUP ========== */
.app-mockup-section {
  padding: 20px 20px 60px;
  display: flex;
  justify-content: center;
}

.app-mockup-img {
  width: 100%;
  max-width: 900px;
  border-radius: 16px;
  box-shadow: 0 20px 60px rgba(0, 0, 0, 0.12);
  display: block;
}

/* ========== FEATURES SECTION ========== */
.features-section {
  padding: 80px 20px;
  max-width: 1200px;
  margin: 0 auto;
}

.section-header {
  text-align: center;
  margin-bottom: 60px;
}

.section-header h2 {
  font-size: 40px;
  font-weight: 700;
  letter-spacing: -0.02em;
  margin-bottom: 12px;
}

.section-header p {
  font-size: 17px;
  color: var(--text-secondary);
  max-width: 600px;
  margin: 0 auto;
  line-height: 1.7;
}

/* ========== FEATURES TABS ========== */
.features-tabs {
  display: flex;
  justify-content: center;
  gap: 8px;
  margin-bottom: 60px;
  flex-wrap: wrap;
}

.tab-btn {
  padding: 10px 24px;
  border: 1.5px solid var(--border-color);
  background: var(--bg-white);
  border-radius: 50px;
  font-size: 15px;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.25s ease;
  font-family: inherit;
}

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

.tab-btn.active {
  background: var(--blue-primary);
  border-color: var(--blue-primary);
  color: #fff;
  font-weight: 500;
}

.tab-content {
  display: none;
}

.tab-content.active {
  display: block;
  animation: fadeUp 0.4s ease;
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(16px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ========== FEATURE CARDS ========== */
.feature-card {
  display: flex;
  align-items: center;
  gap: 60px;
  margin-bottom: 80px;
  padding: 40px;
  background: var(--bg-white);
  border-radius: 24px;
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.03);
  overflow: hidden;
}

.feature-card:last-child {
  margin-bottom: 0;
}

.feature-card.reverse {
  flex-direction: row-reverse;
}

.feature-text {
  flex: 1;
  min-width: 280px;
}

.feature-number {
  font-size: 14px;
  color: var(--text-light);
  font-weight: 500;
  margin-bottom: 8px;
}

.feature-text h3 {
  font-size: 28px;
  font-weight: 700;
  line-height: 1.35;
  margin-bottom: 12px;
  letter-spacing: -0.01em;
}

.feature-text p {
  font-size: 15px;
  color: var(--text-secondary);
  line-height: 1.7;
}

.feature-visual {
  flex: 1.2;
  min-width: 280px;
}

.feature-visual img {
  width: 100%;
  border-radius: var(--radius-md);
  display: block;
}

/* ========== BOTTOM CTA ========== */
.cta-section {
  text-align: center;
  padding: 80px 20px 60px;
  background: var(--bg-page);
}

.cta-section h2 {
  font-size: 36px;
  font-weight: 700;
  margin-bottom: 32px;
  letter-spacing: -0.01em;
}

/* ========== FOOTER ========== */
.footer {
  background: #1a1a1a;
  color: #aaa;
  padding: 32px 40px;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
  font-size: 13px;
  gap: 16px;
}

.footer-info {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  align-items: center;
}

.footer-info span {
  white-space: nowrap;
}

.footer-links {
  display: flex;
  gap: 24px;
}

.footer-links a {
  color: #aaa;
  text-decoration: none;
  transition: color 0.2s;
}

.footer-links a:hover {
  color: #fff;
}

/* ========== PAGE HERO (sub-pages) ========== */
.page-hero {
  text-align: center;
  padding: 130px 20px 50px;
  background: var(--bg-page);
}

.page-hero h1 {
  font-size: 42px;
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.2;
  margin-bottom: 12px;
  color: var(--text-primary);
}

.page-hero p {
  font-size: 17px;
  color: var(--text-secondary);
  max-width: 540px;
  margin: 0 auto;
  line-height: 1.7;
}

/* ========== CHANGELOG ========== */
.changelog-section {
  max-width: 800px;
  margin: 0 auto;
  padding: 0 20px 80px;
}

.changelog-item {
  position: relative;
  padding: 32px 36px;
  background: var(--bg-white);
  border-radius: 20px;
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.03);
  margin-bottom: 24px;
}

.changelog-item::before {
  content: "";
  position: absolute;
  left: -28px;
  top: 40px;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--blue-primary);
  border: 3px solid var(--bg-page);
}

.changelog-timeline {
  position: relative;
  padding-left: 40px;
}

.changelog-timeline::before {
  content: "";
  position: absolute;
  left: -23px;
  top: 0;
  bottom: 0;
  width: 2px;
  background: var(--border-color);
}

.changelog-head {
  display: flex;
  align-items: center;
  gap: 12px;
  margin-bottom: 16px;
  flex-wrap: wrap;
}

.version-badge {
  display: inline-block;
  padding: 4px 14px;
  background: var(--blue-primary);
  color: #fff;
  border-radius: 50px;
  font-size: 14px;
  font-weight: 600;
}

.version-date {
  font-size: 13px;
  color: var(--text-light);
}

.changelog-item h3 {
  font-size: 20px;
  font-weight: 600;
  margin-bottom: 14px;
  color: var(--text-primary);
}

.change-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.change-list li {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  font-size: 15px;
  color: var(--text-secondary);
  line-height: 1.6;
}

.change-tag {
  display: inline-block;
  padding: 2px 10px;
  border-radius: 50px;
  font-size: 12px;
  font-weight: 500;
  white-space: nowrap;
  flex-shrink: 0;
  margin-top: 2px;
}

.change-tag.new {
  background: #e8f5e9;
  color: #2e7d32;
}

.change-tag.improve {
  background: #e3f2fd;
  color: #1565c0;
}

.change-tag.fix {
  background: #fff3e0;
  color: #e65100;
}

/* ========== ARTICLES ========== */
.articles-section {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px 80px;
}

.articles-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
}

.article-card {
  background: var(--bg-white);
  border-radius: 20px;
  overflow: hidden;
  box-shadow: 0 1px 4px rgba(0, 0, 0, 0.03);
  transition: all 0.3s ease;
  text-decoration: none;
  color: inherit;
  display: flex;
  flex-direction: column;
}

.article-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 12px 32px rgba(0, 0, 0, 0.08);
}

.article-cover {
  width: 100%;
  height: 200px;
  object-fit: cover;
  display: block;
}

.article-body {
  padding: 24px;
  flex: 1;
  display: flex;
  flex-direction: column;
}

.article-tag {
  display: inline-block;
  padding: 3px 12px;
  border-radius: 50px;
  font-size: 12px;
  font-weight: 500;
  margin-bottom: 12px;
  align-self: flex-start;
}

.article-tag.guide {
  background: #e3f2fd;
  color: #1565c0;
}

.article-tag.tips {
  background: #e8f5e9;
  color: #2e7d32;
}

.article-tag.news {
  background: #fce4ec;
  color: #c62828;
}

.article-tag.deep {
  background: #f3e5f5;
  color: #6a1b9a;
}

.article-card h3 {
  font-size: 18px;
  font-weight: 600;
  line-height: 1.45;
  margin-bottom: 10px;
  color: var(--text-primary);
}

.article-card p {
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.65;
  flex: 1;
}

.article-meta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: 16px;
  padding-top: 14px;
  border-top: 1px solid var(--border-color);
  font-size: 13px;
  color: var(--text-light);
}

/* ========== RESPONSIVE ========== */
@media (max-width: 900px) {
  .hero h1 {
    font-size: 32px;
  }

  .section-header h2 {
    font-size: 30px;
  }

  .feature-card {
    flex-direction: column !important;
    gap: 30px;
    padding: 24px;
  }

  .feature-text,
  .feature-visual {
    min-width: unset;
    width: 100%;
  }

  .feature-text h3 {
    font-size: 24px;
  }

  .nav-links {
    display: none;
  }

  .cta-section h2 {
    font-size: 26px;
  }

  .page-hero h1 {
    font-size: 30px;
  }

  .articles-grid {
    grid-template-columns: 1fr;
  }

  .changelog-timeline {
    padding-left: 30px;
  }

  .changelog-item {
    padding: 24px;
  }

  .footer {
    flex-direction: column;
    text-align: center;
    padding: 32px 20px;
  }

  .footer-info {
    justify-content: center;
  }
}

@media (max-width: 600px) {
  .hero h1 {
    font-size: 26px;
  }

  .btn-download {
    padding: 12px 28px;
    font-size: 16px;
  }

  .page-hero h1 {
    font-size: 26px;
  }

  .articles-grid {
    gap: 16px;
  }
}