/* 优化版 style.css - 移动端性能优化 + 夜间模式 */
/* 注意：关键CSS已内联到HTML中，此文件延迟加载 */

/* 让页面内跳转变成平滑滚动动画 */
html {
  scroll-behavior: smooth;
}

/*=============== CSS VARIABLES ===============*/
:root {
  --header-height: 3.5rem;

  /* 基础背景色系 */
  --body-color: #FAFBFC;
  --body-color-alt: #F1F5F9;
  --container-color: #FFFFFF;
  --border-color: #E2E8F0;
  --border-color-light: #F1F5F9;

  /* 主色系 */
  --primary-color: #FA8C16;
  --primary-color-alt: #FF6B35;
  --primary-color-light: rgba(250, 140, 22, 0.1);
  --primary-color-lighter: rgba(250, 140, 22, 0.05);
  --primary-color-lightest: rgba(250, 140, 22, 0.03);

  /* 辅色系 */
  --secondary-color: #0EA5E9;
  --secondary-color-light: #5BBDDD;
  --secondary-color-lighter: rgba(14, 165, 233, 0.1);

  /* 点缀色系 */
  --accent-purple: #8B5CF6;
  --accent-purple-light: rgba(139, 92, 246, 0.1);
  --accent-green: #10B981;
  --accent-red: #EF4444;

  /* 渐变色系 */
  --gradient-primary: linear-gradient(135deg, #FA8C16, #FF6B35);
  --gradient-secondary: linear-gradient(135deg, #0EA5E9, #5BBDDD);
  --gradient-accent: linear-gradient(135deg, #8B5CF6 0%, #0EA5E9 100%);

  /* 文字色系 */
  --title-color: #0F172A;
  --text-color: #475569;
  --text-color-light: #94A3B8;

  /* 英雄区专用 */
  --hero-download-bg: #FCF2E6;

  /* Font */
  --body-font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --h1-font-size: 2.25rem;
  --h2-font-size: 1.5rem;
  --h3-font-size: 1.25rem;
  --normal-font-size: 1rem;
  --small-font-size: .875rem;
  --smaller-font-size: .813rem;
  --footer-logo-text-size: 1.1rem;

  --font-regular: 400;
  --font-medium: 500;
  --font-semi-bold: 600;
  --font-bold: 700;

  /* Margins */
  --mb-0-25: .25rem;
  --mb-0-5: .5rem;
  --mb-0-75: .75rem;
  --mb-1: 1rem;
  --mb-1-5: 1.5rem;
  --mb-2: 2rem;
  --mb-2-5: 2.5rem;
  --mb-3: 3rem;
  --mb-4: 4rem;

  /* Border Radius */
  --radius-sm: .25rem;
  --radius-md: .5rem;
  --radius-lg: .75rem;
  --radius-xl: 1rem;
  --radius-pill: 50px;

  /* Box Shadow */
  --shadow-light: 0 4px 15px rgba(15, 23, 42, 0.08);
  --shadow-medium: 0 6px 20px rgba(15, 23, 42, 0.12);
  --shadow-strong: 0 8px 25px rgba(15, 23, 42, 0.15);
  --shadow-enhanced: 0 8px 25px rgba(0,0,0,0.1);
  --shadow-button-primary: 0 4px 15px rgba(250, 140, 22, 0.4);
  --shadow-button-secondary: 0 4px 15px rgba(14, 165, 233, 0.4);

  /* z index */
  --z-tooltip: 10;
  --z-fixed: 100;
  --z-modal: 1000;
}

/* 夜间模式变量 */
body.dark-mode {
  --body-color: #0F172A;
  --body-color-alt: #1E293B;
  --container-color: #1E293B;
  --border-color: #475569;
  --border-color-light: #334155;
  
  --title-color: #F1F5F9;
  --text-color: #CBD5E1;
  --text-color-light: #94A3B8;
  
  --hero-download-bg: #1E293B;
  
  --shadow-light: 0 4px 15px rgba(0, 0, 0, 0.3);
  --shadow-medium: 0 6px 20px rgba(0, 0, 0, 0.4);
  --shadow-strong: 0 8px 25px rgba(0, 0, 0, 0.5);
  --shadow-enhanced: 0 8px 25px rgba(0,0,0,0.4);
}

/* 国产浏览器降级：不用毛玻璃 */
@supports not (backdrop-filter: blur(10px)) {
  .header-scrolled {
    background-color: rgba(255, 255, 255, 0.98) !important;
  }
  body.dark-mode .header-scrolled {
    background-color: rgba(15, 23, 42, 0.98) !important;
  }
}

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

body {
  font-family: var(--body-font);
  font-size: var(--normal-font-size);
  background-color: var(--body-color);
  color: var(--text-color);
  line-height: 1.6;
  overflow-x: hidden;
  transition: background-color 0.3s ease, color 0.3s ease;
}

h1, h2, h3 {
  color: var(--title-color);
  font-weight: var(--font-semi-bold);
  transition: color 0.3s ease;
}

ul { list-style: none; }

a {
  text-decoration: none;
  color: inherit;
  transition: color .3s;
}
a:hover { color: var(--secondary-color); }

img, video {
  max-width: 100%;
  height: auto;
  display: block;
}

button {
  cursor: pointer;
  border: none;
  outline: none;
  font-family: inherit;
}

/*=============== REUSABLE CLASSES ===============*/
.container {
  max-width: 1024px;
  margin-left: auto;
  margin-right: auto;
  padding-left: 1rem;
  padding-right: 1rem;
}

.grid {
  display: grid;
  gap: 1.5rem;
}

.section {
  padding-top: 4.5rem;
  padding-bottom: 2.5rem;
}

.section__header {
  text-align: center;
  margin-bottom: var(--mb-2-5);
}

.section__title {
  font-size: var(--h2-font-size);
  color: var(--title-color);
  margin-bottom: 0;
}

/* 新增：section标题提示文字样式 */
.section__subtitle {
  font-size: var(--small-font-size);
  color: var(--text-color-light);
  margin-top: var(--mb-0-5);
  display: block;
  font-weight: var(--font-regular);
}

.highlight { color: var(--primary-color); }
.brand-name {
  font-weight: var(--font-bold);
  color: var(--title-color);
}

/*=============== 夜间模式切换按钮 ===============*/
.theme-toggle {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background-color: transparent;
  border: none;
  cursor: pointer;
  transition: all 0.3s ease;
  font-size: 1.25rem;
  color: var(--text-color);
  position: relative;
}

.theme-toggle:hover {
  background-color: var(--primary-color-light);
  transform: scale(1.05);
}

.theme-toggle:active {
  transform: scale(0.95);
}

.theme-toggle i {
  transition: transform 0.3s ease;
}

body.dark-mode .theme-toggle:hover {
  background-color: rgba(250, 140, 22, 0.2);
}

/*=============== BUTTONS ===============*/
.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.8rem 1.5rem;
  border-radius: var(--radius-pill);
  font-weight: var(--font-medium);
  transition: all .3s ease;
  text-align: center;
  white-space: nowrap;
}

.button i {
  font-size: 1.1em;
  margin-left: var(--mb-0-5);
}

.button--primary {
  background: var(--gradient-primary);
  color: #fff;
  box-shadow: var(--shadow-button-primary);
}
.button--primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(250, 140, 22, 0.5);
  color: white;
}

.button--secondary {
  background: var(--gradient-secondary);
  color: #fff;
  box-shadow: var(--shadow-button-secondary);
}
.button--secondary:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(14, 165, 233, 0.5);
  color: white;
}

/*=============== NAVIGATION ===============*/
.nav__menu-wrapper {
  display: flex;
  align-items: center;
  column-gap: 1.5rem;
}

/* 移动端默认隐藏菜单 - 修复版 */
@media screen and (max-width: 991px) {
  .nav__menu-wrapper {
    position: fixed !important;
    background-color: hsla(210, 40%, 98%, 0.9);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    top: -150% !important;
    left: 0;
    width: 100%;
    padding: 4rem 1.5rem 3rem;
    border-radius: 0 0 1.5rem 1.5rem;
    box-shadow: var(--shadow-medium);
    transition: top .4s cubic-bezier(0.25, 0.8, 0.25, 1);
    z-index: var(--z-fixed);
    display: flex !important;
    flex-direction: column;
    align-items: stretch;
    row-gap: 1.5rem;
    visibility: hidden;
    opacity: 0;
  }
  
  body.dark-mode .nav__menu-wrapper {
    background-color: hsla(220, 40%, 10%, 0.95);
  }
  
  .nav__menu-wrapper.show-menu {
    top: 0 !important;
    visibility: visible;
    opacity: 1;
  }
}

.nav__menu {
  display: flex;
  align-items: center;
  column-gap: 2rem;
}

.nav__link {
  color: var(--text-color);
  font-weight: var(--font-medium);
  transition: color .3s;
  padding: .5rem 0;
  position: relative;
}
.nav__link:hover { color: var(--secondary-color); }
.nav__link.active-link {
  color: var(--secondary-color);
  font-weight: var(--font-semi-bold);
}

.nav__toggle {
  font-size: 1.5rem;
  color: var(--title-color);
  cursor: pointer;
  display: none;
  z-index: calc(var(--z-fixed) + 1);
}

.nav__toggle i {
  pointer-events: none;
}

/*=============== HERO - 补充样式 ===============*/
.hero__status-text {
  color: var(--text-color-light);
  margin-bottom: var(--mb-2-5);
}

/*=============== FEATURES SECTION ===============*/
#features {
  background-color: var(--body-color-alt);
}

.features-categories {
  display: grid;
  gap: var(--mb-2);
}

.feature-category {
  background-color: var(--container-color);
  border-radius: var(--radius-xl);
  overflow: hidden;
  box-shadow: var(--shadow-light);
  border: 1px solid var(--border-color);
  transition: background-color 0.3s ease, border-color 0.3s ease;
}

body.dark-mode .feature-category {
  border: 1px solid var(--border-color);
}

.category-header {
  padding: var(--mb-1-5) var(--mb-1-5) var(--mb-1);
  border-bottom: 2px solid var(--border-color-light);
}

.category-header-content {
  display: flex;
  align-items: center;
  gap: var(--mb-1);
}

.category-icon-wrapper {
  width: 50px;
  height: 50px;
  border-radius: var(--radius-lg);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.category-icon {
  font-size: 1.75rem;
  color: white;
}

.category-info { flex: 1; }

.category-title {
  font-size: var(--h3-font-size);
  color: var(--title-color);
  margin-bottom: var(--mb-0-25);
  font-weight: var(--font-semi-bold);
}

.category-description {
  font-size: var(--small-font-size);
  color: var(--text-color-light);
  line-height: 1.5;
}

/* 配色方案 */
.category-exam .category-icon-wrapper {
  background: var(--gradient-primary);
}

.category-learning .category-icon-wrapper {
  background: var(--gradient-secondary);
}

.category-training .category-icon-wrapper {
  background: var(--gradient-accent);
}

/* 功能列表 */
.category-features {
  padding: var(--mb-1) var(--mb-1-5) var(--mb-1-5);
}

.feature-items {
  display: grid;
  gap: var(--mb-0-75);
}

.feature-item {
  background-color: var(--body-color-alt);
  padding: var(--mb-1);
  border-radius: var(--radius-md);
  border-left: 3px solid transparent;
  display: flex;
  align-items: flex-start;
  gap: var(--mb-0-75);
  cursor: default;
  pointer-events: none;
  transition: background-color 0.3s ease;
}

body.dark-mode .feature-item {
  background-color: #0F172A;
  border: 1px solid var(--border-color-light);
}

body.dark-mode .feature-item {
  background-color: #0F172A;
  border: 1px solid var(--border-color-light);
}

body.dark-mode .category-exam .feature-item {
  border-left: 3px solid var(--primary-color);
}

body.dark-mode .category-learning .feature-item {
  border-left: 3px solid var(--secondary-color);
}

body.dark-mode .category-training .feature-item {
  border-left: 3px solid var(--accent-purple);
}

.category-exam .feature-item {
  border-left-color: var(--primary-color);
}

.category-learning .feature-item {
  border-left-color: var(--secondary-color);
}

.category-training .feature-item {
  border-left-color: var(--accent-purple);
}

.feature-item-icon {
  flex-shrink: 0;
  width: 32px;
  height: 32px;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.1rem;
}

.category-exam .feature-item-icon {
  background: var(--primary-color-lighter);
  color: var(--primary-color);
}

.category-learning .feature-item-icon {
  background: var(--secondary-color-lighter);
  color: var(--secondary-color);
}

.category-training .feature-item-icon {
  background: var(--accent-purple-light);
  color: var(--accent-purple);
}

.feature-item-content { flex: 1; }

.feature-item-title {
  font-size: var(--normal-font-size);
  color: var(--title-color);
  font-weight: var(--font-semi-bold);
  margin-bottom: var(--mb-0-25);
}

.feature-item-description {
  font-size: var(--small-font-size);
  color: var(--text-color);
  line-height: 1.5;
}

/* 移动端滑动指示器 - 默认隐藏 */
.swiper-indicator {
  display: none;
}

.swipe-hint {
  display: none;
}

/*=============== PRE-REGISTER SECTION ===============*/
.pre-register__container {
  text-align: center;
  max-width: 600px;
  margin: 0 auto;
}

.pre-register__description {
  margin-bottom: var(--mb-2);
  color: var(--text-color);
}

.pre-register__form {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  max-width: 400px;
  margin: 0 auto;
}

.pre-register__form-input {
  width: 100%;
  padding: 0.9rem 1.2rem;
  border: 2px solid var(--border-color);
  border-radius: var(--radius-pill);
  font-size: var(--normal-font-size);
  color: var(--text-color);
  background-color: var(--container-color);
  transition: border-color .3s, box-shadow .3s, background-color 0.3s ease;
}

body.dark-mode .pre-register__form-input {
  border-color: var(--border-color);
}

.pre-register__form-input:focus {
  outline: none;
  border-color: var(--primary-color);
  box-shadow: 0 0 0 3px var(--primary-color-lighter);
}

.pre-register__form .button { width: 100%; }

/*=============== PAST PAPERS SECTION ===============*/
#past-papers {
  background-color: var(--body-color-alt);
}

.papers-cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: var(--mb-2);
}

.paper-card {
  background-color: var(--container-color);
  border-radius: var(--radius-xl);
  padding: var(--mb-2);
  box-shadow: var(--shadow-enhanced);
  border: 2px solid var(--border-color-light);
  transition: all 0.3s ease;
  text-align: center;
  position: relative;
  overflow: hidden;
}

body.dark-mode .paper-card {
  border: 2px solid var(--border-color);
}

.paper-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
}

.paper-card:hover {
  transform: translateY(-5px);
  box-shadow: var(--shadow-strong);
}

.paper-card--cet4::before { background: var(--gradient-primary); }
.paper-card--cet4:hover { border-color: var(--primary-color); }

.paper-card--cet6::before { background: var(--gradient-secondary); }
.paper-card--cet6:hover { border-color: var(--secondary-color); }

.paper-card--pgee::before { background: var(--gradient-accent); }
.paper-card--pgee:hover { border-color: var(--accent-purple); }

.paper-card__icon {
  width: 80px;
  height: 80px;
  margin: 0 auto var(--mb-1);
  border-radius: var(--radius-lg);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 2.5rem;
  color: white;
}

.paper-card--cet4 .paper-card__icon { background: var(--gradient-primary); }
.paper-card--cet6 .paper-card__icon { background: var(--gradient-secondary); }
.paper-card--pgee .paper-card__icon { background: var(--gradient-accent); }

.paper-card__title {
  font-size: var(--h3-font-size);
  color: var(--title-color);
  font-weight: var(--font-semi-bold);
  margin-bottom: var(--mb-0-75);
}

.paper-card__years {
  font-size: var(--normal-font-size);
  color: var(--text-color);
  margin-bottom: var(--mb-0-5);
}

.paper-card__count {
  font-size: var(--h2-font-size);
  font-weight: var(--font-bold);
  margin-bottom: var(--mb-0-25);
}

.paper-card--cet4 .paper-card__count { color: var(--primary-color); }
.paper-card--cet6 .paper-card__count { color: var(--secondary-color); }
.paper-card--pgee .paper-card__count { color: var(--accent-purple); }

.paper-card__label {
  font-size: var(--small-font-size);
  color: var(--text-color-light);
}

/* Papers指示器 - 默认隐藏 */
.papers-indicator {
  display: none;
}

.papers-swipe-hint {
  display: none;
}

/*=============== FOOTER ===============*/
.footer {
  background-color: var(--body-color-alt);
  padding-top: 4rem;
  border-top: 1px solid var(--border-color);
  transition: background-color 0.3s ease, border-color 0.3s ease;
}

.footer__container {
  grid-template-columns: 1fr;
  gap: 2rem;
  padding-bottom: 1.5rem;
}

.footer__info p {
  color: var(--text-color-light);
  line-height: 1.6;
  margin-bottom: var(--mb-0-25);
}

.footer__company-info {
  font-size: var(--smaller-font-size);
  font-weight: var(--font-medium);
  color: var(--text-color);
}

.footer__license-info {
  font-size: var(--smaller-font-size);
  color: var(--text-color-light);
}

.footer__license-info a {
  color: var(--text-color-light);
}
.footer__license-info a:hover {
  color: var(--secondary-color);
  text-decoration: underline;
}

.footer__ga-beian {
  display: flex;
  align-items: center;
}

.ga-beian-icon {
  height: 1em;
  width: auto;
  margin-right: .15rem;
  vertical-align: middle;
}

.footer__legal-links { 
  margin-top: var(--mb-0-5);
  display: flex;
  gap: var(--mb-1);
  flex-wrap: wrap;
}

.footer__legal-links a {
  font-size: var(--smaller-font-size);
}

.footer__contact-link {
  cursor: pointer;
}

.footer__copy {
  display: block;
  margin-top: 0.5rem;
  padding: 1rem 0;
  text-align: center;
  font-size: var(--smaller-font-size);
  color: var(--text-color-light);
  border-top: 1px solid var(--border-color-light);
}

/*=============== SCROLL UP ===============*/
.scrollup {
  position: fixed;
  right: 1rem;
  bottom: -30%;
  background: var(--gradient-primary);
  opacity: .9;
  padding: .5rem .7rem;
  border-radius: var(--radius-sm);
  z-index: var(--z-tooltip);
  transition: .4s;
  box-shadow: var(--shadow-button-primary);
}
.scrollup:hover {
  opacity: 1;
  transform: translateY(-3px);
  box-shadow: 0 6px 20px rgba(250, 140, 22, 0.5);
}
.scrollup__icon {
  font-size: 1.2rem;
  color: #fff;
}
.show-scroll { bottom: 3rem; }

/*=============== FADE IN ANIMATION ===============*/
.fade-in-element {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s ease-out, transform 0.6s ease-out;
  will-change: opacity, transform;
}

.fade-in-element.is-visible {
  opacity: 1;
  transform: translateY(0);
}

/*=============== MOBILE BREAKPOINT (< 768px) ===============*/
@media screen and (max-width: 767px) {
  /* Header优化 */
  .header { box-shadow: 0 2px 8px rgba(15, 23, 42, 0.06); }
  .header-scrolled { box-shadow: 0 2px 12px rgba(15, 23, 42, 0.1); }

  .nav__container {
    padding-left: var(--mb-1);
    padding-right: var(--mb-1);
  }

  .nav__logo-icon { height: 26px; }
  .nav__logo-text { font-size: 1rem; }

  .theme-toggle {
    width: 36px;
    height: 36px;
    font-size: 1.1rem;
  }

  .nav__toggle {
    font-size: 1.75rem;
    padding: 0.25rem;
    display: flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    border-radius: var(--radius-sm);
  }
  .nav__toggle:active { background-color: var(--primary-color-lighter); }

  /* Features - 移动端滑动优化 */
  .category-header {
    padding: var(--mb-1) var(--mb-1-5);
    border-bottom: none;
  }

  .category-icon-wrapper {
    width: 40px;
    height: 40px;
  }

  .category-icon { font-size: 1.5rem; }
  .category-title { font-size: var(--normal-font-size); }
  .category-description { display: none; }

  .category-features { 
    padding: 0;
    overflow: hidden;
  }

  .feature-items {
    display: flex;
    gap: 1rem;
    overflow-x: auto;
    scroll-snap-type: x mandatory;
    -webkit-overflow-scrolling: touch;
    scrollbar-width: none;
    -ms-overflow-style: none;
    /* 修正 */
    padding: var(--mb-1) calc(50vw - 140px);
    scroll-padding: 0;
  }

  .feature-items::-webkit-scrollbar { display: none; }

  .feature-item {
    flex: 0 0 280px;
    scroll-snap-align: center;
    scroll-snap-stop: always;
    flex-direction: column;
    align-items: stretch;
    padding: var(--mb-1-5);
    border-left: none;
    border-top: 3px solid;
    min-height: 180px;
    pointer-events: none;
  }

  body.dark-mode .feature-item {
    border: 1px solid var(--border-color-light);
  }

  .category-exam .feature-item { border-top-color: var(--primary-color); }
  .category-learning .feature-item { border-top-color: var(--secondary-color); }
  .category-training .feature-item { border-top-color: var(--accent-purple); }

  body.dark-mode .category-exam .feature-item { 
    border-top: 3px solid var(--primary-color); 
  }
  body.dark-mode .category-learning .feature-item { 
    border-top: 3px solid var(--secondary-color); 
  }
  body.dark-mode .category-training .feature-item { 
    border-top: 3px solid var(--accent-purple); 
  }

  .feature-item-icon {
    width: 40px;
    height: 40px;
    font-size: 1.25rem;
    margin-bottom: var(--mb-0-5);
  }

  .feature-item-title {
    font-size: var(--h3-font-size);
    margin-bottom: var(--mb-0-5);
  }

  .feature-item-description { font-size: var(--normal-font-size); }

  /* 滑动指示器 */
  .swiper-indicator {
    display: flex;
    justify-content: center;
    gap: 6px;
    padding: var(--mb-1) 0;
    margin-top: var(--mb-0-5);
  }

  .swiper-dot {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background-color: var(--border-color);
    transition: all 0.3s ease;
    cursor: pointer;
  }

  .swiper-dot.active {
    width: 24px;
    border-radius: 4px;
  }

  .category-exam .swiper-dot.active { background-color: var(--primary-color); }
  .category-learning .swiper-dot.active { background-color: var(--secondary-color); }
  .category-training .swiper-dot.active { background-color: var(--accent-purple); }

  /* 不显示滑动提示 */
  .swipe-hint {
    display: none !important;
  }

  /* Papers - 移动端滑动优化，默认居中显示六级 */
  .papers-cards {
    display: flex;
    gap: 1rem;
    overflow-x: auto;
    scroll-snap-type: x mandatory;
    -webkit-overflow-scrolling: touch;
    scrollbar-width: none;
    -ms-overflow-style: none;
    /* 修正 */
    padding: 0 calc(50vw - 140px);
    scroll-padding: 0;
  }

  .papers-cards::-webkit-scrollbar { display: none; }

  .paper-card {
    flex: 0 0 280px;
    scroll-snap-align: center;
    scroll-snap-stop: always;
    min-height: 280px;
  }

  .paper-card__icon {
    width: 90px;
    height: 90px;
    font-size: 2.75rem;
  }

  .paper-card__title { font-size: var(--h2-font-size); }
  .paper-card__years { font-size: var(--h3-font-size); }
  .paper-card__count { font-size: 2.5rem; }

  .papers-indicator {
    display: flex;
    justify-content: center;
    gap: 6px;
    padding: var(--mb-1) 0;
    margin-top: var(--mb-1);
  }

  .papers-dot {
    width: 8px;
    height: 8px;
    border-radius: 50%;
    background-color: var(--border-color);
    transition: all 0.3s ease;
    cursor: pointer;
  }

  .papers-dot.active {
    width: 24px;
    border-radius: 4px;
  }

  .papers-dot:nth-child(1).active { background-color: var(--primary-color); }
  .papers-dot:nth-child(2).active { background-color: var(--secondary-color); }
  .papers-dot:nth-child(3).active { background-color: var(--accent-purple); }

  /* 不显示Papers滑动提示 */
  .papers-swipe-hint {
    display: none !important;
  }

  /* Footer优化 */
  .footer { padding-top: 2.5rem; }

  .footer__container {
    grid-template-columns: 1fr;
    gap: var(--mb-1-5);
    padding-bottom: 1rem;
  }

  .footer__info {
    text-align: center;
    padding-bottom: var(--mb-1-5);
  }

  .footer__company-info {
    font-size: var(--small-font-size);
    margin-bottom: var(--mb-0-5);
  }

  .footer__license-info { font-size: var(--smaller-font-size); }
  .footer__ga-beian { justify-content: center; }

  .footer__legal-links {
    display: flex;
    justify-content: center;
    gap: var(--mb-1);
    flex-wrap: wrap;
  }
  
  .footer__copy {
    margin-top: 0;
    padding: 0.75rem 0;
  }

  /* 预约表单优化 */
  .pre-register__container { padding: 0 var(--mb-1); }

  .pre-register__description {
    font-size: var(--normal-font-size);
    line-height: 1.8;
    padding: 0 var(--mb-0-5);
  }

  .pre-register__form {
    max-width: 100%;
    padding: 0 var(--mb-0-5);
  }

  .pre-register__form-input {
    font-size: var(--normal-font-size);
    padding: 1rem 1.2rem;
  }

  .pre-register__form .button {
    padding: 1rem 2rem;
    font-size: var(--normal-font-size);
  }

  /* Section间距优化 */
  .section {
    padding-top: 3.5rem;
    padding-bottom: 2rem;
  }

  .section__header {
    margin-bottom: var(--mb-2);
    padding: 0 var(--mb-1);
  }

  .section__title {
    font-size: var(--h2-font-size);
    line-height: 1.4;
  }

  /* 移动端：subtitle单独一行，字号稍小 */
  .section__subtitle {
    font-size: var(--smaller-font-size);
    margin-top: var(--mb-0-5);
  }
}

/*=============== EXTRA SMALL MOBILE (< 360px) ===============*/
@media screen and (max-width: 360px) {
  .container {
    margin-left: var(--mb-0-75);
    margin-right: var(--mb-0-75);
    padding-left: var(--mb-0-75);
    padding-right: var(--mb-0-75);
  }

  .nav__container {
    padding-left: var(--mb-0-75);
    padding-right: var(--mb-0-75);
  }

  .nav__logo-text { display: none; }
  .nav__logo-icon { height: 24px; }

  .theme-toggle {
    width: 32px;
    height: 32px;
    font-size: 1rem;
  }

  .nav__toggle {
    width: 36px;
    height: 36px;
    font-size: 1.5rem;
  }

  .hero__main-title {
    font-size: 1.5rem;
    padding: 0 var(--mb-0-25);
  }

  .hero__sub-title {
    font-size: 0.875rem;
    padding: 0 var(--mb-0-5);
  }

  .hero__container .button {
    width: 95%;
    padding: 0.875rem 1.5rem;
    font-size: var(--small-font-size);
  }

  .section__title { font-size: 1.375rem; }

  .pre-register__form-input,
  .pre-register__form .button {
    font-size: var(--small-font-size);
    padding: 0.875rem 1rem;
  }

  /* 超小屏幕卡片优化 */
  .feature-item {
    flex: 0 0 260px;
  }

  /* 修正超小屏幕下的padding */
  .feature-items {
    padding: var(--mb-1) calc(50vw - 130px);
  }

  .paper-card {
    flex: 0 0 260px;
  }

  /* 修正超小屏幕下的padding */
  .papers-cards {
    padding: 0 calc(50vw - 130px);
  }
}

/*=============== TABLET (>= 768px) ===============*/
@media screen and (min-width: 768px) {
  .container {
    padding-left: 1.5rem;
    padding-right: 1.5rem;
  }

  .section {
    padding-top: 5.5rem;
    padding-bottom: 3.5rem;
  }

  .feature-items {
    grid-template-columns: repeat(2, 1fr);
  }

  .pre-register__form {
    flex-direction: row;
  }

  .pre-register__form .button {
    width: auto;
  }

  .footer__info { text-align: center; }
  .footer__ga-beian { justify-content: center; }
  .footer__legal-links { justify-content: center; }

  /* 平板及以上：subtitle仍然单独一行 */
  .section__subtitle {
    font-size: var(--small-font-size);
    margin-top: var(--mb-0-5);
  }
}

/*=============== DESKTOP MENU (<= 991px) ===============*/
@media screen and (max-width: 991px) {
  .nav__menu {
    flex-direction: column;
    align-items: stretch;
    row-gap: 1rem;
    width: 100%;
  }

  .nav__item { width: 100%; }

  .nav__link {
    display: block;
    text-align: center;
    padding: 0.75rem 1rem;
    color: var(--title-color);
    font-weight: var(--font-semi-bold);
    border-radius: var(--radius-sm);
  }

  .nav__link:hover {
    background-color: var(--secondary-color-lighter);
    color: var(--secondary-color);
  }

  .nav__link.active-link {
    background-color: var(--secondary-color-lighter);
  }

  .nav__toggle { display: inline-flex; margin-left: auto; }
}

/*=============== LARGE DESKTOP (>= 992px) ===============*/
@media screen and (min-width: 992px) {
  :root {
    --header-height: calc(3.5rem + .5rem);
    --h1-font-size: 2.75rem;
    --h2-font-size: 1.75rem;
    --h3-font-size: 1.375rem;
    --normal-font-size: 1.063rem;
    --small-font-size: .938rem;
    --smaller-font-size: .875rem;
    --footer-logo-text-size: 1.15rem;
  }

  .container { max-width: 968px; }

  .section {
    padding-top: 6.5rem;
    padding-bottom: 2.5rem;
  }

  .nav__container { height: calc(var(--header-height) + 0.5rem); }
  .nav__logo-icon { height: 32px; }
  .nav__logo-text { display: inline; }
  .nav__menu-wrapper { display: flex; }
  .nav__menu { column-gap: 3rem; }
  .nav__link { font-size: var(--normal-font-size); }
  .nav__toggle { display: none; }

  .footer__container { padding-bottom: 4rem; }
  .footer__copy {
    margin-top: 1.5rem;
    font-size: var(--smaller-font-size);
  }

  /* 桌面端：subtitle单独一行 */
  .section__subtitle {
    font-size: var(--small-font-size);
    margin-top: var(--mb-0-75);
  }
}

/*=============== XL DESKTOP (>= 1200px) ===============*/
@media screen and (min-width: 1200px) {
  .container { max-width: 1140px; }
  .footer__container { gap: 2.5rem; }
}

/*=============== XXL DESKTOP (>= 1400px) ===============*/
@media screen and (min-width: 1400px) {
  .container { max-width: 1320px; }
}

/*=============== PERFORMANCE OPTIMIZATIONS ===============*/

/* 减少重绘 */
* {
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* GPU加速 */
.button,
.nav__link,
.paper-card,
.scrollup,
.theme-toggle {
  will-change: transform;
}

/* 移除不必要的动画 - 性能优化 */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

/* 硬件加速 */
.header,
.nav__menu-wrapper,
.scrollup {
  transform: translateZ(0);
  backface-visibility: hidden;
}

/* 优化滚动性能 */
.feature-items,
.papers-cards {
  -webkit-overflow-scrolling: touch;
}

/* 字体渲染优化 */
body {
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* 图片加载优化 */
img {
  content-visibility: auto;
}

/* 延迟渲染优化 */
.section:not(.hero) {
  content-visibility: auto;
  contain-intrinsic-size: 0 500px;
}