/* ==========================================================================
   Luleå tekniska universitet (LTU) Theme
   严格对齐 ltu.se 真实设计
   2026-10-12 v1

   真实设计系统 (从 ltu.se 提取):
   - 主色: deep navy   #032040 (深蓝)
   - 辅色: blue        #17416F (中蓝)
   - 强调: orange     (CTA - 推测 #E87722 类似 CDU)
   - 文字:  #1a1a1a on white
   - 字体:  sans-serif
   - 风格: 大图 hero + 3 矩形深蓝卡片 + 3 浅色子卡片 + 活动横条
   ========================================================================== */

:root {
  --ltu-navy:        #032040;
  --ltu-navy-dark:   #021430;
  --ltu-navy-mid:    #17416F;
  --ltu-blue:        #2a4a8c;
  --ltu-blue-light:  #4a6aa3;
  --ltu-orange:      #E87722;
  --ltu-ink:         #1a1a1a;
  --ltu-grey-50:     #f5f7fa;
  --ltu-grey-100:    #e5e8ed;
  --ltu-grey-700:    #4a5266;
  --ltu-white:        #ffffff;

  --ltu-font-body:    "Source Sans Pro", "Inter", "Helvetica Neue", -apple-system, "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  --ltu-font-heading: var(--ltu-font-body);

  --ltu-s-xxs: .25rem; --ltu-s-xs: .5rem;  --ltu-s-s:  1rem;
  --ltu-s-m:  1.5rem; --ltu-s-l:  2rem;   --ltu-s-xl: 2.5rem;
  --ltu-s-xxl: 3rem;  --ltu-s-xxxl: 4rem;  --ltu-s-xxxxl: 5rem;

  --ltu-radius:       0;
  --ltu-radius-md:    4px;
  --ltu-t:            200ms ease;
  --ltu-container:    1280px;
}

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

body {
  margin: 0;
  font-family: var(--ltu-font-body);
  font-size: 16px;
  line-height: 1.6;
  color: var(--ltu-ink);
  background: var(--ltu-white);
  -webkit-font-smoothing: antialiased;
}

img { max-width: 100%; display: block; }
a { color: var(--ltu-blue); text-decoration: none; transition: color var(--ltu-t); }
a:hover { color: var(--ltu-navy); text-decoration: underline; }

h1, h2, h3, h4, h5, h6 {
  margin: 0 0 var(--ltu-s-s);
  font-family: var(--ltu-font-heading);
  font-weight: 700;
  line-height: 1.2;
  color: var(--ltu-navy);
}
h1 { font-size: clamp(2rem, 4.5vw, 3rem); }
h2 { font-size: clamp(1.5rem, 3vw, 2.25rem); }
h3 { font-size: 1.25rem; }
p { margin: 0 0 var(--ltu-s-s); }


/* ===== Site Header (LTU 真实: 深蓝 navy + 白 logo) ===== */
.site-header {
  background: var(--ltu-navy);
  position: sticky;
  top: 0;
  z-index: 50;
}
.site-header__top {
  background: var(--ltu-navy);
  color: var(--ltu-white);
}
.site-header__top-inner {
  max-width: var(--ltu-container);
  margin: 0 auto;
  padding: 0.75rem var(--ltu-s-s);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--ltu-s-s);
}
.site-brand { display: inline-flex; align-items: center; text-decoration: none; }
.site-brand__img { height: 40px; width: auto; }
.site-header__top-right {
  display: flex;
  align-items: center;
  gap: var(--ltu-s-l);
}
.site-header__top-link {
  color: var(--ltu-white);
  text-decoration: none;
  font-size: 0.875rem;
  font-weight: 500;
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
}
.site-header__top-link:hover { color: var(--ltu-orange); text-decoration: none; }
.site-header__menu-btn {
  background: transparent;
  color: var(--ltu-white);
  border: 1px solid var(--ltu-white);
  padding: 0.3rem 0.75rem;
  font-size: 0.875rem;
  cursor: pointer;
}
.site-header__menu-btn:hover { background: var(--ltu-white); color: var(--ltu-navy); }


/* ===== Hero (LTU 真实: 全屏实景 + 右侧白色 CTA 框) ===== */
.home-hero {
  position: relative;
  min-height: 540px;
  background: var(--ltu-navy);
  overflow: hidden;
}
.home-hero__image {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
  z-index: 0;
}
.home-hero__overlay {
  position: relative;
  z-index: 2;
  background: linear-gradient(90deg, rgba(3,32,64,0.5) 0%, rgba(3,32,64,0.2) 100%);
  color: var(--ltu-white);
  padding: var(--ltu-s-xxxxl) var(--ltu-s-s);
  min-height: 540px;
  display: flex;
  align-items: center;
  max-width: var(--ltu-container);
  margin: 0 auto;
}
.home-hero__cta {
  background: var(--ltu-white);
  color: var(--ltu-navy);
  padding: var(--ltu-s-l) var(--ltu-s-xl);
  border-top: 4px solid var(--ltu-orange);
  max-width: 360px;
  margin-left: auto;
}
.home-hero__title {
  font-family: var(--ltu-font-heading);
  font-size: clamp(1.5rem, 3vw, 2.25rem);
  font-weight: 700;
  line-height: 1.2;
  color: var(--ltu-navy);
  margin: 0 0 var(--ltu-s-s);
  text-transform: uppercase;
}
.home-hero__btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.75rem 1.5rem;
  background: var(--ltu-orange);
  color: var(--ltu-white);
  border-radius: var(--ltu-radius-md);
  text-decoration: none;
  font-weight: 700;
  font-size: 0.9375rem;
}
.home-hero__btn:hover { background: #d56a18; color: var(--ltu-white); text-decoration: none; }


/* ===== Buttons ===== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  padding: 0.75rem 1.5rem;
  font-family: var(--ltu-font-body);
  font-size: 0.9375rem;
  font-weight: 700;
  border-radius: var(--ltu-radius-md);
  border: 1.5px solid transparent;
  cursor: pointer;
  transition: all var(--ltu-t);
  text-decoration: none;
  line-height: 1.2;
}
.btn--primary {
  background: var(--ltu-orange);
  color: var(--ltu-white);
  border-color: var(--ltu-orange);
}
.btn--primary:hover { background: #d56a18; border-color: #d56a18; color: var(--ltu-white); text-decoration: none; }
.btn--outline {
  background: transparent;
  color: var(--ltu-white);
  border-color: var(--ltu-white);
}
.btn--outline:hover { background: var(--ltu-white); color: var(--ltu-navy); text-decoration: none; }
.btn--navy {
  background: var(--ltu-navy);
  color: var(--ltu-white);
  border-color: var(--ltu-navy);
}
.btn--navy:hover { background: var(--ltu-navy-dark); border-color: var(--ltu-navy-dark); color: var(--ltu-white); text-decoration: none; }
.btn--white {
  background: var(--ltu-white);
  color: var(--ltu-navy);
  border-color: var(--ltu-white);
}
.btn--white:hover { background: var(--ltu-grey-50); color: var(--ltu-navy); text-decoration: none; }


/* ===== Sections ===== */
.section {
  width: 100%;
  padding: var(--ltu-s-xxxxl) var(--ltu-s-s);
}
.section--white { background: var(--ltu-white); }
.section--grey { background: var(--ltu-grey-50); }
.section--navy { background: var(--ltu-navy); color: var(--ltu-white); }
.section--navy h1, .section--navy h2, .section--navy h3 { color: var(--ltu-white); }
.section__container { max-width: var(--ltu-container); margin: 0 auto; }
.section__head { margin-bottom: var(--ltu-s-xl); }
.section__head--center { text-align: center; }
.section__title {
  font-size: clamp(1.5rem, 3vw, 2.25rem);
  font-weight: 700;
  color: var(--ltu-navy);
  margin: 0 0 var(--ltu-s-s);
}
.section--navy .section__title { color: var(--ltu-white); }
.section__sub {
  font-size: 1.0625rem;
  color: var(--ltu-grey-700);
  max-width: 48rem;
  margin: 0;
}
.section--navy .section__sub { color: rgba(255,255,255,0.88); }


/* ===== 3 矩形深蓝卡片 (LTU 真实) ===== */
.feature-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--ltu-s-m);
  max-width: var(--ltu-container);
  margin: 0 auto;
  padding: 0 var(--ltu-s-s);
}
.feature-card {
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  background: var(--ltu-navy);
  color: var(--ltu-white);
  text-decoration: none;
  padding: var(--ltu-s-l);
  min-height: 280px;
  position: relative;
  overflow: hidden;
  transition: background var(--ltu-t);
}
.feature-card::before {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(180deg, transparent 0%, rgba(3,32,64,0.85) 100%);
  z-index: 0;
}
.feature-card:hover { background: var(--ltu-navy-dark); color: var(--ltu-white); text-decoration: none; }
.feature-card__eyebrow {
  position: relative;
  z-index: 1;
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  color: var(--ltu-orange);
  margin: 0 0 var(--ltu-s-xs);
}
.feature-card__title {
  position: relative;
  z-index: 1;
  font-family: var(--ltu-font-heading);
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--ltu-white);
  margin: 0;
  line-height: 1.3;
}


/* ===== 3 浅色子卡片 (LTU 真实) ===== */
.subfeature-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--ltu-s-m);
  max-width: var(--ltu-container);
  margin: 0 auto;
  padding: 0 var(--ltu-s-s);
}
.subfeature-card {
  display: flex;
  flex-direction: column;
  background: var(--ltu-grey-50);
  text-decoration: none;
  color: var(--ltu-ink);
  overflow: hidden;
  transition: transform var(--ltu-t);
}
.subfeature-card:hover { transform: translateY(-2px); color: var(--ltu-ink); text-decoration: none; }
.subfeature-card__media {
  width: 100%;
  aspect-ratio: 4/3;
  background: linear-gradient(135deg, var(--ltu-navy) 0%, var(--ltu-blue) 100%);
  display: flex;
  align-items: center;
  justify-content: center;
  color: rgba(255,255,255,0.5);
  font-size: 2.5rem;
}
.subfeature-card__body { padding: var(--ltu-s-m); }
.subfeature-card__title {
  font-family: var(--ltu-font-heading);
  font-size: 1.125rem;
  font-weight: 700;
  color: var(--ltu-navy);
  margin: 0 0 0.5rem;
  line-height: 1.3;
}
.subfeature-card__body p {
  font-size: 0.875rem;
  color: var(--ltu-grey-700);
  margin: 0 0 var(--ltu-s-s);
  line-height: 1.5;
}
.subfeature-card__cta {
  display: inline-flex;
  align-items: center;
  gap: 0.25rem;
  font-size: 0.875rem;
  font-weight: 700;
  color: var(--ltu-blue);
  text-decoration: underline;
}


/* ===== Stats 4 列 ===== */
.stats-bar {
  background: var(--ltu-navy);
  color: var(--ltu-white);
  padding: var(--ltu-s-xxl) var(--ltu-s-s);
}
.stats-bar__inner {
  max-width: var(--ltu-container);
  margin: 0 auto;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--ltu-s-l);
  text-align: center;
}
.stat__num {
  font-family: var(--ltu-font-heading);
  font-size: 2.5rem;
  font-weight: 700;
  color: var(--ltu-orange);
  line-height: 1;
  margin: 0 0 0.25rem;
}
.stat__label {
  font-size: 0.875rem;
  color: rgba(255,255,255,0.92);
  margin: 0;
}


/* ===== Calendar 活动横条 (LTU 真实) ===== */
.calendar {
  max-width: var(--ltu-container);
  margin: 0 auto;
  padding: 0 var(--ltu-s-s);
}
.calendar__row {
  display: grid;
  grid-template-columns: 200px 1fr 200px;
  gap: var(--ltu-s-m);
  align-items: center;
  background: var(--ltu-white);
  border: 1px solid var(--ltu-grey-100);
  border-left: 4px solid var(--ltu-orange);
  padding: var(--ltu-s-m);
  margin-bottom: var(--ltu-s-s);
  text-decoration: none;
  color: var(--ltu-ink);
  transition: all var(--ltu-t);
}
.calendar__row:hover { transform: translateX(2px); box-shadow: 0 2px 8px rgba(0,0,0,0.06); color: var(--ltu-ink); text-decoration: none; }
.calendar__date {
  text-align: center;
  font-weight: 700;
  color: var(--ltu-navy);
  font-size: 0.875rem;
}
.calendar__date-day { font-size: 1.5rem; display: block; }
.calendar__title {
  font-family: var(--ltu-font-heading);
  font-size: 1.0625rem;
  font-weight: 700;
  color: var(--ltu-navy);
  margin: 0;
  line-height: 1.3;
}
.calendar__type {
  font-size: 0.75rem;
  color: var(--ltu-grey-700);
  text-transform: uppercase;
  text-align: right;
  letter-spacing: 0.05em;
}


/* ===== News 3-col ===== */
.news-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--ltu-s-m);
  max-width: var(--ltu-container);
  margin: 0 auto;
  padding: 0 var(--ltu-s-s);
}
.news-card {
  display: flex;
  flex-direction: column;
  text-decoration: none;
  color: var(--ltu-ink);
  background: var(--ltu-white);
  border: 1px solid var(--ltu-grey-100);
  border-top: 4px solid var(--ltu-navy);
  overflow: hidden;
  transition: all var(--ltu-t);
}
.news-card:hover { transform: translateY(-2px); box-shadow: 0 4px 12px rgba(0,0,0,0.08); color: var(--ltu-ink); text-decoration: none; }
.news-card__media {
  width: 100%;
  aspect-ratio: 16/10;
  background: linear-gradient(135deg, var(--ltu-navy) 0%, var(--ltu-blue) 100%);
}
.news-card__body { padding: var(--ltu-s-m); }
.news-card__date {
  font-size: 0.75rem;
  color: var(--ltu-grey-700);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin: 0 0 0.5rem;
}
.news-card__title {
  font-family: var(--ltu-font-heading);
  font-size: 1.0625rem;
  font-weight: 700;
  color: var(--ltu-navy);
  line-height: 1.3;
  margin: 0 0 var(--ltu-s-s);
}
.news-card__cta {
  display: inline-flex;
  align-items: center;
  gap: 0.25rem;
  font-size: 0.875rem;
  font-weight: 700;
  color: var(--ltu-orange);
  text-decoration: underline;
  margin-top: auto;
}


/* ===== Page Hero (内页) ===== */
.page-hero {
  background: var(--ltu-navy);
  color: var(--ltu-white);
  padding: var(--ltu-s-xl) var(--ltu-s-s);
  border-bottom: 4px solid var(--ltu-orange);
}
.page-hero__container { max-width: var(--ltu-container); margin: 0 auto; }
.page-hero__breadcrumb {
  font-size: 0.875rem;
  color: rgba(255,255,255,0.7);
  margin: 0 0 var(--ltu-s-s);
}
.page-hero__breadcrumb a { color: var(--ltu-white); }
.page-hero__title {
  font-family: var(--ltu-font-heading);
  font-size: clamp(1.75rem, 3vw, 2.5rem);
  font-weight: 700;
  color: var(--ltu-white);
  margin: 0 0 var(--ltu-s-s);
}
.page-hero__sub {
  font-size: 1.0625rem;
  color: rgba(255,255,255,0.88);
  max-width: 48rem;
  margin: 0;
}


/* ===== Content (prose) ===== */
.page-content {
  max-width: var(--ltu-container);
  margin: 0 auto;
  padding: var(--ltu-s-xxxxl) var(--ltu-s-s);
}
.prose {
  max-width: 56rem;
  font-size: 1.0625rem;
  line-height: 1.7;
  color: var(--ltu-ink);
}
.prose h2 {
  font-size: 1.625rem;
  color: var(--ltu-navy);
  margin: var(--ltu-s-xl) 0 var(--ltu-s-s);
  border-bottom: 3px solid var(--ltu-orange);
  padding-bottom: 0.5rem;
  display: inline-block;
}
.prose h3 { font-size: 1.25rem; color: var(--ltu-navy); margin: var(--ltu-s-l) 0 var(--ltu-s-xs); }
.prose a { color: var(--ltu-blue); text-decoration: underline; }
.prose blockquote {
  border-left: 4px solid var(--ltu-orange);
  padding: 0.5rem var(--ltu-s-m);
  margin: var(--ltu-s-m) 0;
  background: var(--ltu-grey-50);
  font-style: italic;
}


/* ===== Footer (LTU 真实: 深蓝 + 4 列) ===== */
.site-footer {
  background: var(--ltu-navy);
  color: var(--ltu-white);
  padding: var(--ltu-s-xxxxl) var(--ltu-s-s) var(--ltu-s-l);
}
.site-footer__grid {
  max-width: var(--ltu-container);
  margin: 0 auto var(--ltu-s-xl);
  display: grid;
  grid-template-columns: 2fr 1fr 1fr 1fr;
  gap: var(--ltu-s-l);
}
.site-footer__col h4 {
  font-size: 0.875rem;
  font-weight: 700;
  color: var(--ltu-orange);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin: 0 0 var(--ltu-s-s);
}
.site-footer__col p {
  font-size: 0.875rem;
  color: rgba(255,255,255,0.85);
  margin: 0 0 var(--ltu-s-xs);
  line-height: 1.5;
}
.site-footer__col ul { list-style: none; padding: 0; margin: 0; }
.site-footer__col li { margin: 0 0 var(--ltu-s-xs); }
.site-footer__col a {
  color: rgba(255,255,255,0.85);
  text-decoration: none;
  font-size: 0.875rem;
}
.site-footer__col a:hover { color: var(--ltu-orange); text-decoration: underline; }
.site-footer__network {
  max-width: var(--ltu-container);
  margin: 0 auto var(--ltu-s-l);
  padding: var(--ltu-s-m) 0;
  border-top: 1px solid rgba(255,255,255,0.15);
  border-bottom: 1px solid rgba(255,255,255,0.15);
}
.site-footer__network-label {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  color: rgba(255,255,255,0.6);
  letter-spacing: 0.1em;
  margin: 0 0 var(--ltu-s-xs);
}
.site-footer__network ul {
  list-style: none;
  padding: 0;
  margin: 0;
  display: flex;
  flex-wrap: wrap;
  gap: var(--ltu-s-xs) var(--ltu-s-m);
}
.site-footer__network a {
  color: rgba(255,255,255,0.85);
  text-decoration: none;
  font-size: 0.8125rem;
}
.site-footer__network a:hover { color: var(--ltu-orange); text-decoration: underline; }
.site-footer__bottom {
  max-width: var(--ltu-container);
  margin: 0 auto;
  padding-top: var(--ltu-s-l);
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: var(--ltu-s-s);
  font-size: 0.8125rem;
  color: rgba(255,255,255,0.7);
}
.site-footer__bottom a { color: rgba(255,255,255,0.85); text-decoration: underline; }


/* ===== Responsive ===== */
@media (max-width: 1024px) {
  .feature-grid, .subfeature-grid, .news-grid { grid-template-columns: repeat(2, 1fr); }
  .site-footer__grid { grid-template-columns: repeat(2, 1fr); }
  .stats-bar__inner { grid-template-columns: repeat(2, 1fr); }
  .calendar__row { grid-template-columns: 150px 1fr; }
  .calendar__type { display: none; }
}
@media (max-width: 640px) {
  .site-header__top-inner { padding: 0.5rem var(--ltu-s-s); }
  .feature-grid, .subfeature-grid, .news-grid, .site-footer__grid { grid-template-columns: 1fr; }
  .stats-bar__inner { grid-template-columns: repeat(2, 1fr); }
  .section { padding: var(--ltu-s-xl) var(--ltu-s-s); }
  .home-hero__overlay { padding: var(--ltu-s-l) var(--ltu-s-s); }
  .home-hero__cta { margin: 0 auto; }
}