/* ============================================
   Design Theory Page - 设计论页面样式
   ============================================ */

.design-theory-page {
  background: #ffffff;
}

/* 强制设计论页面header使用深色文字（适应白色hero背景） */
.design-theory-page .main-header:not(.sticky) {
  background: transparent;
}

.design-theory-page .main-header:not(.sticky) .nav__link,
.design-theory-page .main-header:not(.sticky) .header-lang-toggle,
.design-theory-page .main-header:not(.sticky) .header-fullscreen-toggle {
  color: #000000 !important;
}

.design-theory-page .main-header:not(.sticky) .logo-img {
  filter: none !important;
}

.design-theory-page .main-header:not(.sticky) .hamburger__line {
  background: #242424 !important;
}

.design-theory-page .page-content-wrapper {
  position: relative;
  z-index: 100;
  width: 100%;
  background: #ffffff;
}

/* services-hero 在设计论页面的底部间距修正 */
.design-theory-page .services-hero {
  margin-bottom: 0;
}


/* ============================================
   容器
   ============================================ */
.dt-container {
  max-width: 1440px;
  margin: 0 auto;
  padding: 0 60px;
}

@media (max-width: 1024px) {
  .dt-container {
    padding: 0 40px;
  }
}

@media (max-width: 768px) {
  .dt-container {
    padding: 0 24px;
  }
}


/* ============================================
   区块标题
   ============================================ */
.dt-section-header {
  margin-bottom: 48px;
}

.dt-section-label {
  display: block;
  font-size: 13px;
  font-weight: 500;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: #999;
  margin-bottom: 12px;
}

.dt-section-title {
  font-size: 40px;
  font-weight: 700;
  color: #111;
  margin: 0 0 16px;
  line-height: 1.2;
}

.dt-section-desc {
  font-size: 16px;
  color: #666;
  margin: 0;
  max-width: 560px;
  line-height: 1.6;
}

@media (max-width: 768px) {
  .dt-section-header {
    margin-bottom: 32px;
  }
  .dt-section-title {
    font-size: 28px;
  }
  .dt-section-desc {
    font-size: 15px;
  }
}

/* ============================================
   文章列表
   ============================================ */
.dt-articles {
  padding: 100px 0;
  background: #f5f5f5;
  margin-bottom: 0;
}

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

.dt-articles__grid .dt-article-card--featured {
  grid-column: span 2;
}

@media (max-width: 1024px) {
  .dt-articles__grid {
    grid-template-columns: repeat(2, 1fr);
  }
  .dt-articles__grid .dt-article-card--featured {
    grid-column: span 2;
  }
}

@media (max-width: 640px) {
  .dt-articles {
    padding: 60px 0;
  }
  .dt-articles__grid {
    grid-template-columns: 1fr;
  }
  .dt-articles__grid .dt-article-card--featured {
    grid-column: span 1;
  }
}

/* ============================================
   文章卡片
   ============================================ */
.dt-article-card {
  display: flex;
  flex-direction: column;
  background: #fff;
  border-radius: 16px;
  overflow: hidden;
  text-decoration: none;
  transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.dt-article-card:hover {
  transform: translateY(-4px);
  box-shadow: 0 16px 48px rgba(0, 0, 0, 0.1);
}

.dt-article-card__image {
  width: 100%;
  aspect-ratio: 16 / 9;
  overflow: hidden;
  background: #eee;
}

.dt-article-card--featured .dt-article-card__image {
  aspect-ratio: 21 / 9;
}

.dt-article-card__image img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  transition: transform 0.5s ease;
}

.dt-article-card:hover .dt-article-card__image img {
  transform: scale(1.04);
}

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

.dt-article-card__tags {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 12px;
}

.dt-tag {
  font-size: 11px;
  font-weight: 500;
  color: #001166;
  background: rgba(0, 17, 102, 0.07);
  padding: 3px 10px;
  border-radius: 20px;
  letter-spacing: 0.02em;
}

.dt-article-card__title {
  font-size: 18px;
  font-weight: 600;
  color: #111;
  line-height: 1.4;
  margin: 0 0 10px;
}

.dt-article-card--featured .dt-article-card__title {
  font-size: 22px;
}

.dt-article-card__summary {
  font-size: 14px;
  color: #666;
  line-height: 1.6;
  margin: 0 0 auto;
  flex: 1;
}

.dt-article-card__meta {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-top: 20px;
  padding-top: 16px;
  border-top: 1px solid #f0f0f0;
}

.dt-article-card__date {
  font-size: 12px;
  color: #999;
  font-variant-numeric: tabular-nums;
}

.dt-article-card__arrow {
  color: #111;
  display: flex;
  align-items: center;
  transition: transform 0.2s ease;
}

.dt-article-card:hover .dt-article-card__arrow {
  transform: translate(2px, -2px);
}

@media (max-width: 768px) {
  .dt-article-card__body {
    padding: 20px;
  }
  .dt-article-card__title {
    font-size: 16px;
  }
  .dt-article-card--featured .dt-article-card__title {
    font-size: 18px;
  }
}

/* ============================================
   FAQ 区块
   ============================================ */
.dt-faq {
  padding: 100px 0;
  background: #ffffff;
  margin-bottom: var(--footer-h, 80vh);
}

.dt-faq__group-title {
  font-size: 14px;
  font-weight: 600;
  color: #001166;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  margin: 32px 0 16px;
  padding-bottom: 8px;
  border-bottom: 2px solid rgba(0, 17, 102, 0.12);
}

.dt-faq__list {
  display: flex;
  flex-direction: column;
  gap: 0;
  border-radius: 16px;
  overflow: hidden;
  border: 1px solid #e8e8e8;
  margin-bottom: 24px;
}

.dt-faq__item {
  border-bottom: 1px solid #e8e8e8;
}

.dt-faq__item:last-child {
  border-bottom: none;
}

.dt-faq__question {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 24px 28px;
  background: #fff;
  border: none;
  cursor: pointer;
  text-align: left;
  font-size: 16px;
  font-weight: 600;
  color: #111;
  font-family: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  transition: background 0.15s ease;
  line-height: 1.5;
}

.dt-faq__question:hover {
  background: #fafafa;
}

.dt-faq__icon {
  flex-shrink: 0;
  color: #666;
  transition: transform 0.25s ease;
}

.dt-faq__item.is-open .dt-faq__icon {
  transform: rotate(180deg);
}

.dt-faq__answer {
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.35s cubic-bezier(0.4, 0, 0.2, 1);
}

.dt-faq__answer-inner {
  padding: 0 28px 24px;
  font-size: 15px;
  color: #555;
  line-height: 1.8;
  font-family: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  border-top: 1px dashed #e8e8e8;
  padding-top: 20px;
  margin: 0 28px;
}

@media (max-width: 768px) {
  .dt-faq {
    padding: 60px 0;
  }
  .dt-faq__question {
    padding: 20px 20px;
    font-size: 15px;
  }
  .dt-faq__answer-inner {
    padding: 16px 20px 20px;
    margin: 0 0;
    font-size: 14px;
  }
}

/* ============================================
   空状态
   ============================================ */
.dt-empty {
  padding: 120px 0;
  margin-bottom: var(--footer-h, 80vh);
}

.dt-empty__inner {
  text-align: center;
  color: #999;
  font-size: 16px;
}

.dt-btn {
  display: inline-flex;
  align-items: center;
  margin-top: 24px;
  padding: 14px 32px;
  background: #111;
  color: #fff;
  border-radius: 8px;
  text-decoration: none;
  font-size: 15px;
  font-weight: 500;
  transition: background 0.2s ease;
}

.dt-btn:hover {
  background: #333;
}

/* ============================================
   文章正文中穿插的问答样式
   视觉上融入文章，不显眼，AI可识别结构
   ============================================ */
.dt-inline-qa {
  margin: 24px 0;
  padding: 0 0 0 20px;
  border-left: 3px solid #e8e8e8;
}

.dt-qa-q {
  font-size: 15px;
  color: #444;
  margin: 0 0 8px;
  line-height: 1.6;
}

.dt-qa-a {
  font-size: 14px;
  color: #666;
  margin: 0;
  line-height: 1.8;
}

/* 文章详情页正文样式 */
.dt-article-content {
  font-size: 16px;
  color: #333;
  line-height: 1.9;
}

.dt-article-content h2 {
  font-size: 20px;
  font-weight: 700;
  color: #111;
  margin: 36px 0 16px;
}

.dt-article-content h3 {
  font-size: 17px;
  font-weight: 600;
  color: #222;
  margin: 28px 0 12px;
}

.dt-article-content p {
  margin: 0 0 18px;
}

.dt-article-content strong {
  color: #111;
  font-weight: 600;
}

/* ============================================
   知识库卡片（隐藏式语料）
   ============================================ */
.dt-knowledge {
  padding: 100px 0;
  background: #ffffff;
  margin-bottom: var(--footer-h, 80vh);
}

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

.dt-knowledge__card {
  background: #f8f9fc;
  border-radius: 12px;
  padding: 28px;
  border: 1px solid #e8e8e8;
  transition: box-shadow 0.2s ease;
}

.dt-knowledge__card:hover {
  box-shadow: 0 4px 20px rgba(0,0,0,0.06);
}

.dt-knowledge__card-title {
  font-size: 15px;
  font-weight: 600;
  color: #111;
  margin: 0 0 12px;
  line-height: 1.5;
}

.dt-knowledge__card-body {
  font-size: 14px;
  color: #555;
  line-height: 1.8;
  margin: 0 0 16px;
}

.dt-knowledge__card-tag {
  display: inline-block;
  font-size: 11px;
  color: #001166;
  background: rgba(0,17,102,0.07);
  padding: 3px 10px;
  border-radius: 20px;
}

/* 有文章时，知识库不需要额外间距 */
.dt-articles + .dt-knowledge {
  margin-bottom: var(--footer-h, 80vh);
}

@media (max-width: 1024px) {
  .dt-knowledge__grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 640px) {
  .dt-knowledge {
    padding: 60px 0;
  }
  .dt-knowledge__grid {
    grid-template-columns: 1fr;
  }
}