/* ============================================================
   b2s01k04n03-summit- 全站样式
   网络议题问答索引站 - 课程学院海报级大标题，语气创作者友好
   Mobile-First 响应式设计
   ============================================================ */

/* CSS Reset & Base */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --b2s01k04n03-summit-primary: #1a3a5c;
  --b2s01k04n03-summit-secondary: #2d6a4f;
  --b2s01k04n03-summit-accent: #e07a3a;
  --b2s01k04n03-summit-bg: #fafbfc;
  --b2s01k04n03-summit-card-bg: #ffffff;
  --b2s01k04n03-summit-text: #2c3e50;
  --b2s01k04n03-summit-text-light: #5a6c7d;
  --b2s01k04n03-summit-border: #e2e8f0;
  --b2s01k04n03-summit-shadow: 0 2px 8px rgba(26,58,92,0.08);
  --b2s01k04n03-summit-shadow-lg: 0 8px 32px rgba(26,58,92,0.12);
  --b2s01k04n03-summit-radius: 6px;
  --b2s01k04n03-summit-font-heading: 'Noto Serif SC', 'Georgia', serif;
  --b2s01k04n03-summit-font-body: 'Noto Sans SC', 'Helvetica Neue', Arial, sans-serif;
  --b2s01k04n03-summit-max-width: 1200px;
  --b2s01k04n03-summit-transition: 0.25s cubic-bezier(0.23,1,0.32,1);
}

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

body {
  font-family: var(--b2s01k04n03-summit-font-body);
  color: var(--b2s01k04n03-summit-text);
  background-color: var(--b2s01k04n03-summit-bg);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

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

a {
  color: var(--b2s01k04n03-summit-primary);
  text-decoration: none;
  transition: color var(--b2s01k04n03-summit-transition);
}

a:hover {
  color: var(--b2s01k04n03-summit-accent);
}

ul, ol {
  list-style: none;
}

/* ============================================================
   Typography
   ============================================================ */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--b2s01k04n03-summit-font-heading);
  color: var(--b2s01k04n03-summit-primary);
  line-height: 1.3;
  font-weight: 700;
}

h1 { font-size: 2.2rem; margin-bottom: 1rem; }
h2 { font-size: 1.8rem; margin-bottom: 0.8rem; }
h3 { font-size: 1.4rem; margin-bottom: 0.6rem; }
h4 { font-size: 1.2rem; margin-bottom: 0.5rem; }

p {
  margin-bottom: 1rem;
  line-height: 1.8;
}

blockquote {
  border-left: 4px solid var(--b2s01k04n03-summit-accent);
  padding: 1rem 1.5rem;
  margin: 1.5rem 0;
  background: rgba(224,122,58,0.05);
  font-style: italic;
  border-radius: 0 var(--b2s01k04n03-summit-radius) var(--b2s01k04n03-summit-radius) 0;
}

/* ============================================================
   Layout
   ============================================================ */
.b2s01k04n03-summit-container {
  width: 100%;
  max-width: var(--b2s01k04n03-summit-max-width);
  margin: 0 auto;
  padding: 0 1rem;
}

.b2s01k04n03-summit-section {
  padding: 3rem 0;
}

.b2s01k04n03-summit-section-title {
  text-align: center;
  margin-bottom: 2.5rem;
  position: relative;
}

.b2s01k04n03-summit-section-title::after {
  content: '';
  display: block;
  width: 60px;
  height: 3px;
  background: var(--b2s01k04n03-summit-accent);
  margin: 0.8rem auto 0;
  border-radius: 2px;
}

/* ============================================================
   Header & Navigation
   ============================================================ */
.b2s01k04n03-summit-header {
  background: var(--b2s01k04n03-summit-card-bg);
  border-bottom: 1px solid var(--b2s01k04n03-summit-border);
  position: relative;
  z-index: 100;
}

.b2s01k04n03-summit-header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.8rem 1rem;
  max-width: var(--b2s01k04n03-summit-max-width);
  margin: 0 auto;
}

.b2s01k04n03-summit-logo {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-family: var(--b2s01k04n03-summit-font-heading);
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--b2s01k04n03-summit-primary);
}

.b2s01k04n03-summit-logo img {
  width: 36px;
  height: 36px;
  border-radius: 4px;
}

.b2s01k04n03-summit-nav {
  display: none;
}

.b2s01k04n03-summit-nav ul {
  display: flex;
  gap: 1.5rem;
  align-items: center;
}

.b2s01k04n03-summit-nav a {
  font-size: 0.95rem;
  font-weight: 500;
  padding: 0.4rem 0;
  position: relative;
}

.b2s01k04n03-summit-nav a::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--b2s01k04n03-summit-accent);
  transition: width var(--b2s01k04n03-summit-transition);
}

.b2s01k04n03-summit-nav a:hover::after,
.b2s01k04n03-summit-nav a.active::after {
  width: 100%;
}

.b2s01k04n03-summit-mobile-toggle {
  display: flex;
  flex-direction: column;
  gap: 4px;
  cursor: pointer;
  padding: 0.5rem;
}

.b2s01k04n03-summit-mobile-toggle span {
  display: block;
  width: 22px;
  height: 2px;
  background: var(--b2s01k04n03-summit-primary);
  border-radius: 2px;
  transition: var(--b2s01k04n03-summit-transition);
}

.b2s01k04n03-summit-mobile-nav {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  right: 0;
  background: var(--b2s01k04n03-summit-card-bg);
  border-bottom: 1px solid var(--b2s01k04n03-summit-border);
  box-shadow: var(--b2s01k04n03-summit-shadow-lg);
  z-index: 99;
}

.b2s01k04n03-summit-mobile-nav.active {
  display: block;
}

.b2s01k04n03-summit-mobile-nav ul {
  padding: 1rem;
}

.b2s01k04n03-summit-mobile-nav li {
  border-bottom: 1px solid var(--b2s01k04n03-summit-border);
}

.b2s01k04n03-summit-mobile-nav li:last-child {
  border-bottom: none;
}

.b2s01k04n03-summit-mobile-nav a {
  display: block;
  padding: 0.8rem 0;
  font-size: 1rem;
}

/* ============================================================
   Hero / Banner
   ============================================================ */
.b2s01k04n03-summit-hero {
  position: relative;
  background: linear-gradient(135deg, var(--b2s01k04n03-summit-primary) 0%, #0d2137 100%);
  color: #ffffff;
  padding: 4rem 1rem;
  text-align: center;
  overflow: hidden;
}

.b2s01k04n03-summit-hero::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background: url('../images/banner-hero.webp') center/cover no-repeat;
  opacity: 0.15;
}

.b2s01k04n03-summit-hero-content {
  position: relative;
  z-index: 2;
  max-width: 700px;
  margin: 0 auto;
}

.b2s01k04n03-summit-hero h1 {
  color: #ffffff;
  font-size: 2.4rem;
  margin-bottom: 1.2rem;
  letter-spacing: -0.02em;
}

.b2s01k04n03-summit-hero p {
  font-size: 1.1rem;
  opacity: 0.9;
  margin-bottom: 2rem;
  line-height: 1.8;
}

.b2s01k04n03-summit-cta-btn {
  display: inline-block;
  background: var(--b2s01k04n03-summit-accent);
  color: #ffffff;
  padding: 0.9rem 2.2rem;
  border-radius: var(--b2s01k04n03-summit-radius);
  font-weight: 600;
  font-size: 1rem;
  transition: transform var(--b2s01k04n03-summit-transition), box-shadow var(--b2s01k04n03-summit-transition);
  box-shadow: 0 4px 12px rgba(224,122,58,0.3);
}

.b2s01k04n03-summit-cta-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 20px rgba(224,122,58,0.4);
  color: #ffffff;
}

/* ============================================================
   Cards
   ============================================================ */
.b2s01k04n03-summit-card {
  background: var(--b2s01k04n03-summit-card-bg);
  border: 1px solid var(--b2s01k04n03-summit-border);
  border-radius: var(--b2s01k04n03-summit-radius);
  overflow: hidden;
  box-shadow: var(--b2s01k04n03-summit-shadow);
  transition: transform var(--b2s01k04n03-summit-transition), box-shadow var(--b2s01k04n03-summit-transition);
}

.b2s01k04n03-summit-card:hover {
  transform: translateY(-3px);
  box-shadow: var(--b2s01k04n03-summit-shadow-lg);
}

.b2s01k04n03-summit-card-img {
  width: 100%;
  height: 180px;
  object-fit: cover;
}

.b2s01k04n03-summit-card-body {
  padding: 1.2rem;
}

.b2s01k04n03-summit-card-title {
  font-size: 1.1rem;
  margin-bottom: 0.5rem;
}

.b2s01k04n03-summit-card-meta {
  font-size: 0.85rem;
  color: var(--b2s01k04n03-summit-text-light);
  margin-bottom: 0.6rem;
}

.b2s01k04n03-summit-card-excerpt {
  font-size: 0.92rem;
  color: var(--b2s01k04n03-summit-text-light);
  line-height: 1.6;
}

/* Grid layouts */
.b2s01k04n03-summit-grid-2 {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.5rem;
}

.b2s01k04n03-summit-grid-3 {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.5rem;
}

.b2s01k04n03-summit-grid-4 {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
}

/* ============================================================
   Features / Advantages
   ============================================================ */
.b2s01k04n03-summit-feature-item {
  text-align: center;
  padding: 2rem 1.5rem;
  background: var(--b2s01k04n03-summit-card-bg);
  border-radius: var(--b2s01k04n03-summit-radius);
  border: 1px solid var(--b2s01k04n03-summit-border);
}

.b2s01k04n03-summit-feature-icon {
  width: 56px;
  height: 56px;
  margin: 0 auto 1rem;
  background: linear-gradient(135deg, var(--b2s01k04n03-summit-primary), var(--b2s01k04n03-summit-secondary));
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  color: #ffffff;
  font-size: 1.4rem;
}

/* ============================================================
   FAQ
   ============================================================ */
.b2s01k04n03-summit-faq-item {
  border: 1px solid var(--b2s01k04n03-summit-border);
  border-radius: var(--b2s01k04n03-summit-radius);
  margin-bottom: 1rem;
  overflow: hidden;
}

.b2s01k04n03-summit-faq-question {
  padding: 1rem 1.2rem;
  font-weight: 600;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: var(--b2s01k04n03-summit-card-bg);
  transition: background var(--b2s01k04n03-summit-transition);
}

.b2s01k04n03-summit-faq-question:hover {
  background: rgba(26,58,92,0.03);
}

.b2s01k04n03-summit-faq-answer {
  padding: 0 1.2rem 1rem;
  font-size: 0.95rem;
  line-height: 1.8;
  color: var(--b2s01k04n03-summit-text-light);
  display: none;
}

.b2s01k04n03-summit-faq-item.active .b2s01k04n03-summit-faq-answer {
  display: block;
}

/* ============================================================
   Footer
   ============================================================ */
.b2s01k04n03-summit-footer {
  background: var(--b2s01k04n03-summit-primary);
  color: #c8d6e5;
  padding: 3rem 1rem 1.5rem;
}

.b2s01k04n03-summit-footer-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 2rem;
  max-width: var(--b2s01k04n03-summit-max-width);
  margin: 0 auto;
}

.b2s01k04n03-summit-footer h4 {
  color: #ffffff;
  font-size: 1rem;
  margin-bottom: 1rem;
}

.b2s01k04n03-summit-footer a {
  color: #a0b4c8;
  font-size: 0.9rem;
  display: block;
  padding: 0.25rem 0;
}

.b2s01k04n03-summit-footer a:hover {
  color: #ffffff;
}

.b2s01k04n03-summit-footer-bottom {
  border-top: 1px solid rgba(255,255,255,0.1);
  margin-top: 2rem;
  padding-top: 1.5rem;
  text-align: center;
  font-size: 0.85rem;
  color: #7f9ab5;
}

.b2s01k04n03-summit-footer-social {
  display: flex;
  gap: 1rem;
  margin-top: 0.8rem;
}

.b2s01k04n03-summit-footer-social a {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  background: rgba(255,255,255,0.1);
  color: #c8d6e5;
  font-size: 0.85rem;
  transition: background var(--b2s01k04n03-summit-transition);
}

.b2s01k04n03-summit-footer-social a:hover {
  background: var(--b2s01k04n03-summit-accent);
  color: #ffffff;
}

/* ============================================================
   Breadcrumb
   ============================================================ */
.b2s01k04n03-summit-breadcrumb {
  padding: 1rem;
  font-size: 0.88rem;
  color: var(--b2s01k04n03-summit-text-light);
  max-width: var(--b2s01k04n03-summit-max-width);
  margin: 0 auto;
}

.b2s01k04n03-summit-breadcrumb a {
  color: var(--b2s01k04n03-summit-text-light);
}

.b2s01k04n03-summit-breadcrumb a:hover {
  color: var(--b2s01k04n03-summit-accent);
}

.b2s01k04n03-summit-breadcrumb span {
  margin: 0 0.4rem;
}

/* ============================================================
   Article / Content Page
   ============================================================ */
.b2s01k04n03-summit-article {
  max-width: 800px;
  margin: 0 auto;
  padding: 2rem 1rem;
}

.b2s01k04n03-summit-article-header {
  margin-bottom: 2rem;
}

.b2s01k04n03-summit-article-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  font-size: 0.88rem;
  color: var(--b2s01k04n03-summit-text-light);
  margin-top: 0.8rem;
}

.b2s01k04n03-summit-article-content {
  font-size: 1rem;
  line-height: 1.9;
}

.b2s01k04n03-summit-article-content h2 {
  margin-top: 2rem;
}

.b2s01k04n03-summit-article-content h3 {
  margin-top: 1.5rem;
}

.b2s01k04n03-summit-article-content p {
  margin-bottom: 1.2rem;
}

/* ============================================================
   Form
   ============================================================ */
.b2s01k04n03-summit-form-group {
  margin-bottom: 1.2rem;
}

.b2s01k04n03-summit-form-group label {
  display: block;
  font-weight: 600;
  margin-bottom: 0.4rem;
  font-size: 0.92rem;
}

.b2s01k04n03-summit-form-group input,
.b2s01k04n03-summit-form-group textarea,
.b2s01k04n03-summit-form-group select {
  width: 100%;
  padding: 0.7rem 1rem;
  border: 1px solid var(--b2s01k04n03-summit-border);
  border-radius: var(--b2s01k04n03-summit-radius);
  font-size: 0.95rem;
  font-family: inherit;
  transition: border-color var(--b2s01k04n03-summit-transition);
}

.b2s01k04n03-summit-form-group input:focus,
.b2s01k04n03-summit-form-group textarea:focus,
.b2s01k04n03-summit-form-group select:focus {
  outline: none;
  border-color: var(--b2s01k04n03-summit-primary);
}

.b2s01k04n03-summit-submit-btn {
  display: inline-block;
  background: var(--b2s01k04n03-summit-primary);
  color: #ffffff;
  padding: 0.8rem 2rem;
  border: none;
  border-radius: var(--b2s01k04n03-summit-radius);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: background var(--b2s01k04n03-summit-transition), transform 0.16s ease-out;
}

.b2s01k04n03-summit-submit-btn:hover {
  background: #0d2137;
}

.b2s01k04n03-summit-submit-btn:active {
  transform: scale(0.97);
}

/* ============================================================
   Video Section
   ============================================================ */
.b2s01k04n03-summit-video-wrapper {
  position: relative;
  padding-bottom: 56.25%;
  height: 0;
  overflow: hidden;
  border-radius: var(--b2s01k04n03-summit-radius);
  background: #000;
}

.b2s01k04n03-summit-video-wrapper video {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

/* ============================================================
   Trust / Certification
   ============================================================ */
.b2s01k04n03-summit-trust-badges {
  display: flex;
  flex-wrap: wrap;
  gap: 1.5rem;
  justify-content: center;
  align-items: center;
  padding: 2rem 0;
}

.b2s01k04n03-summit-trust-badge {
  padding: 0.8rem 1.5rem;
  background: var(--b2s01k04n03-summit-card-bg);
  border: 1px solid var(--b2s01k04n03-summit-border);
  border-radius: var(--b2s01k04n03-summit-radius);
  font-size: 0.88rem;
  font-weight: 500;
  color: var(--b2s01k04n03-summit-text);
}

/* ============================================================
   Timeline
   ============================================================ */
.b2s01k04n03-summit-timeline {
  position: relative;
  padding-left: 2rem;
}

.b2s01k04n03-summit-timeline::before {
  content: '';
  position: absolute;
  left: 0.5rem;
  top: 0;
  bottom: 0;
  width: 2px;
  background: var(--b2s01k04n03-summit-border);
}

.b2s01k04n03-summit-timeline-item {
  position: relative;
  margin-bottom: 2rem;
  padding-left: 1rem;
}

.b2s01k04n03-summit-timeline-item::before {
  content: '';
  position: absolute;
  left: -1.6rem;
  top: 0.4rem;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--b2s01k04n03-summit-accent);
  border: 2px solid var(--b2s01k04n03-summit-card-bg);
}

.b2s01k04n03-summit-timeline-year {
  font-weight: 700;
  color: var(--b2s01k04n03-summit-primary);
  margin-bottom: 0.3rem;
}

/* ============================================================
   Interactive Tool (Resource Filter)
   ============================================================ */
.b2s01k04n03-summit-filter-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 0.8rem;
  margin-bottom: 1.5rem;
}

.b2s01k04n03-summit-filter-btn {
  padding: 0.5rem 1.2rem;
  border: 1px solid var(--b2s01k04n03-summit-border);
  border-radius: 20px;
  font-size: 0.88rem;
  cursor: pointer;
  background: var(--b2s01k04n03-summit-card-bg);
  transition: all var(--b2s01k04n03-summit-transition);
}

.b2s01k04n03-summit-filter-btn:hover,
.b2s01k04n03-summit-filter-btn.active {
  background: var(--b2s01k04n03-summit-primary);
  color: #ffffff;
  border-color: var(--b2s01k04n03-summit-primary);
}

/* ============================================================
   Responsive: 480px
   ============================================================ */
@media (min-width: 480px) {
  .b2s01k04n03-summit-grid-2 {
    grid-template-columns: repeat(2, 1fr);
  }
  .b2s01k04n03-summit-footer-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

/* ============================================================
   Responsive: 768px
   ============================================================ */
@media (min-width: 768px) {
  h1 { font-size: 2.6rem; }
  h2 { font-size: 2rem; }

  .b2s01k04n03-summit-container {
    padding: 0 1.5rem;
  }

  .b2s01k04n03-summit-section {
    padding: 4rem 0;
  }

  .b2s01k04n03-summit-hero {
    padding: 5rem 2rem;
  }

  .b2s01k04n03-summit-hero h1 {
    font-size: 2.8rem;
  }

  .b2s01k04n03-summit-grid-3 {
    grid-template-columns: repeat(2, 1fr);
  }

  .b2s01k04n03-summit-grid-4 {
    grid-template-columns: repeat(2, 1fr);
  }

  .b2s01k04n03-summit-footer-grid {
    grid-template-columns: repeat(3, 1fr);
  }
}

/* ============================================================
   Responsive: 992px
   ============================================================ */
@media (min-width: 992px) {
  .b2s01k04n03-summit-nav {
    display: block;
  }

  .b2s01k04n03-summit-mobile-toggle {
    display: none;
  }

  .b2s01k04n03-summit-grid-3 {
    grid-template-columns: repeat(3, 1fr);
  }

  .b2s01k04n03-summit-grid-4 {
    grid-template-columns: repeat(4, 1fr);
  }

  .b2s01k04n03-summit-footer-grid {
    grid-template-columns: repeat(4, 1fr);
  }
}

/* ============================================================
   Responsive: 1200px
   ============================================================ */
@media (min-width: 1200px) {
  .b2s01k04n03-summit-container {
    padding: 0 2rem;
  }

  .b2s01k04n03-summit-hero h1 {
    font-size: 3.2rem;
  }

  .b2s01k04n03-summit-section {
    padding: 5rem 0;
  }
}

/* ============================================================
   Utility Classes
   ============================================================ */
.b2s01k04n03-summit-text-center { text-align: center; }
.b2s01k04n03-summit-mt-1 { margin-top: 0.5rem; }
.b2s01k04n03-summit-mt-2 { margin-top: 1rem; }
.b2s01k04n03-summit-mt-3 { margin-top: 1.5rem; }
.b2s01k04n03-summit-mb-2 { margin-bottom: 1rem; }
.b2s01k04n03-summit-mb-3 { margin-bottom: 1.5rem; }

/* 404 Page */
.b2s01k04n03-summit-404 {
  text-align: center;
  padding: 6rem 1rem;
}

.b2s01k04n03-summit-404 h1 {
  font-size: 5rem;
  color: var(--b2s01k04n03-summit-accent);
}