@import url('https://fonts.googleapis.com/css2?family=Open+Sans:wght@300;400;500;600;700&family=Poppins:wght@400;500;600;700&display=swap');

/* ============================================================
   基础 Reset & 变量
   ============================================================ */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --c-black: #000000;
  --c-white: #ffffff;
  --c-gray-100: #f5f5f5;
  --c-gray-200: #e8e8e8;
  --c-gray-400: #999999;
  --c-gray-700: #333333;
  --font-head: 'Poppins', 'Open Sans', sans-serif;
  --font-body: 'Open Sans', 'Poppins', sans-serif;
  --nav-width: 240px;
  --max-prose: 760px;
  --gap: 2rem;
  --scroll-offset: 72px;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-body);
  font-size: 1rem;
  line-height: 1.7;
  color: var(--c-black);
  background: var(--c-white);
  overflow-x: hidden;
}

/* ============================================================
   页面骨架：侧边导航 + 主内容
   ============================================================ */
.page-shell {
  display: grid;
  grid-template-columns: var(--nav-width) 1fr;
  min-height: 100vh;
  align-items: start;
}

/* ============================================================
   侧边导航
   ============================================================ */
.side-nav {
  position: fixed;
  top: 0;
  left: 0;
  width: var(--nav-width);
  height: 100vh;
  background: var(--c-black);
  color: var(--c-white);
  display: flex;
  flex-direction: column;
  padding: 2rem 1.5rem;
  overflow-y: auto;
  z-index: 100;
  border-right: 3px solid var(--c-black);
}

.side-nav__brand {
  margin-bottom: 2.5rem;
  border-bottom: 1px solid rgba(255,255,255,0.15);
  padding-bottom: 1.5rem;
}

.site-logo img {
  max-width: 140px;
  height: auto;
  display: block;
}

.site-logo-text {
  font-family: var(--font-head);
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--c-white);
  text-decoration: none;
  letter-spacing: 0.04em;
  display: block;
  margin-bottom: 0.5rem;
}

.side-nav__tagline {
  display: block;
  font-size: 0.75rem;
  color: var(--c-gray-400);
  line-height: 1.5;
  margin-top: 0.5rem;
}

.side-nav__menu {
  flex: 1;
}

.side-nav__menu dl {
  list-style: none;
}

.side-nav__menu dt {
  margin-bottom: 0.25rem;
}

.side-nav__menu dt a {
  font-family: var(--font-head);
  font-size: 0.875rem;
  font-weight: 500;
  color: rgba(255,255,255,0.75);
  text-decoration: none;
  padding: 0.75rem 0.75rem;
  border-left: 3px solid transparent;
  letter-spacing: 0.02em;
  transition: color 200ms ease, border-color 200ms ease, background 200ms ease;
  min-height: 44px;
  display: flex;
  align-items: center;
}

.side-nav__menu dt a:hover,
.side-nav__menu dt a:focus {
  color: var(--c-white);
  border-left-color: var(--c-white);
  background: rgba(255,255,255,0.07);
  outline: none;
}

.side-nav__contact {
  margin-top: 2rem;
  border-top: 1px solid rgba(255,255,255,0.1);
  padding-top: 1rem;
}

.contact-item {
  font-size: 0.75rem;
  color: var(--c-gray-400);
  margin-bottom: 0.4rem;
}

.contact-item a {
  color: rgba(255,255,255,0.6);
  text-decoration: none;
  transition: color 200ms;
}

.contact-item a:hover {
  color: var(--c-white);
}

/* ============================================================
   主内容区
   ============================================================ */
.page-main {
  margin-left: var(--nav-width);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ============================================================
   Hero
   ============================================================ */
.hero {
  position: relative;
  min-height: 45vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
  background: var(--c-black);
  color: var(--c-white);
  overflow: hidden;
  padding: 4rem 3rem 5rem;
}

.hero__inner {
  position: relative;
  z-index: 2;
  max-width: var(--max-prose);
  margin: 0 auto;
  text-align: center;
  width: 100%;
}

.hero__eyebrow {
  font-family: var(--font-head);
  font-size: 0.75rem;
  font-weight: 600;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: rgba(255,255,255,0.5);
  margin-bottom: 1rem;
}

.hero__title {
  font-family: var(--font-head);
  font-size: clamp(2rem, 5vw, 3.5rem);
  font-weight: 700;
  line-height: 1.15;
  letter-spacing: -0.02em;
  color: var(--c-white);
  margin-bottom: 1.25rem;
}

.hero__sub {
  font-size: 1rem;
  color: rgba(255,255,255,0.65);
  max-width: 540px;
  margin: 0 auto;
  line-height: 1.7;
}

/* 色带斜切分割 */
.hero__band {
  position: absolute;
  bottom: -2px;
  left: 0;
  width: 100%;
  height: 60px;
  background: var(--c-white);
  clip-path: polygon(0 100%, 100% 100%, 100% 0);
  z-index: 3;
}

/* ============================================================
   主内容
   ============================================================ */
main {
  flex: 1;
}

.wrap {
  max-width: var(--max-prose);
  margin: 0 auto;
  padding: 3rem 2rem 4rem;
}

.content-section {
  width: 100%;
}

/* ============================================================
   正文文章排版
   ============================================================ */
.prose {
  font-family: var(--font-body);
  font-size: 1rem;
  line-height: 1.8;
  color: var(--c-black);
}

.prose h2 {
  font-family: var(--font-head);
  font-size: clamp(1.4rem, 3vw, 1.875rem);
  font-weight: 700;
  line-height: 1.25;
  margin: 3.5rem 0 0.5rem;
  letter-spacing: -0.01em;
  border-top: 3px solid var(--c-black);
  padding-top: 1.5rem;
  scroll-margin-top: var(--scroll-offset);
}

.prose h2:first-child {
  margin-top: 0;
  border-top: none;
  padding-top: 0;
}

.prose p.subtitle,
.prose p.subhead,
.prose p.desc,
.prose p.lead {
  font-size: 1rem;
  color: var(--c-gray-700);
  margin-bottom: 1.5rem;
  font-weight: 500;
}

.prose h3 {
  font-family: var(--font-head);
  font-size: 1.2rem;
  font-weight: 600;
  margin: 2rem 0 0.6rem;
  letter-spacing: 0;
}

.prose p {
  margin-bottom: 1.2rem;
}

.prose ul,
.prose ol {
  margin: 1rem 0 1.2rem 1.5rem;
}

.prose li {
  margin-bottom: 0.5rem;
}

.prose a {
  color: var(--c-black);
  text-decoration: underline;
  text-underline-offset: 3px;
  transition: opacity 200ms;
}

.prose a:hover {
  opacity: 0.6;
}

.prose strong {
  font-weight: 700;
}

.prose em {
  font-style: italic;
}

.prose blockquote {
  border-left: 4px solid var(--c-black);
  padding: 0.75rem 1.25rem;
  margin: 1.5rem 0;
  background: var(--c-gray-100);
  font-style: italic;
}

.prose table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
  font-size: 0.9rem;
}

.prose th,
.prose td {
  border: 1px solid var(--c-gray-200);
  padding: 0.6rem 0.8rem;
  text-align: left;
}

.prose th {
  background: var(--c-black);
  color: var(--c-white);
  font-weight: 600;
}

.prose img {
  max-width: 100%;
  height: auto;
  display: block;
  margin: 1.5rem 0;
}

/* article scroll offset for fixed/sticky nav (single page) */
.prose article,
article[id] {
  scroll-margin-top: var(--scroll-offset);
}

/* ============================================================
   页脚（极简：仅 p + small）
   ============================================================ */
.site-footer {
  background: var(--c-gray-100);
  border-top: 3px solid var(--c-black);
  padding: 2rem 3rem;
  text-align: center;
}

.footer-brand {
  font-family: var(--font-head);
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--c-black);
  margin-bottom: 0.5rem;
}

.footer-copy {
  font-size: 0.78rem;
  color: var(--c-gray-400);
  display: block;
}

/* ============================================================
   动效（stagger list、parallax CSS hint）
   ============================================================ */
@media (prefers-reduced-motion: no-preference) {
  .prose h2,
  .prose h3,
  .prose p,
  .prose li {
    animation: fadeUp 0.4s ease both;
  }

  @keyframes fadeUp {
    from {
      opacity: 0;
      transform: translateY(12px);
    }
    to {
      opacity: 1;
      transform: none;
    }
  }

  .prose > * {
    animation-delay: calc(var(--i, 0) * 60ms);
  }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation: none !important;
    transition: none !important;
  }
  html {
    scroll-behavior: auto;
  }
}

/* ============================================================
   卡片
   ============================================================ */
.card {
  border: 2px solid var(--c-black);
  border-radius: 0;
  padding: 1.5rem;
  background: var(--c-white);
  transition: box-shadow 220ms ease;
}

.card:hover {
  box-shadow: 6px 6px 0 var(--c-black);
}

/* ============================================================
   响应式：移动端
   ============================================================ */
@media (max-width: 768px) {
  :root {
    --nav-width: 0px;
    --scroll-offset: 56px;
  }

  .page-shell {
    grid-template-columns: 1fr;
  }

  .side-nav {
    position: static;
    width: 100%;
    height: auto;
    flex-direction: column;
    padding: 1rem 1.25rem;
    border-right: none;
    border-bottom: 3px solid var(--c-black);
    overflow: visible;
  }

  .side-nav__brand {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin-bottom: 0;
    border-bottom: none;
    padding-bottom: 0;
    flex-wrap: wrap;
  }

  .side-nav__tagline {
    display: none;
  }

  .side-nav__menu {
    margin-top: 0.75rem;
  }

  .side-nav__menu dl {
    display: flex;
    flex-wrap: wrap;
    gap: 0.25rem;
  }

  .side-nav__menu dt {
    margin-bottom: 0;
  }

  .side-nav__menu dt a {
    font-size: 0.85rem;
    padding: 0.65rem 0.9rem;
    border-left: none;
    border-bottom: 2px solid transparent;
    min-height: 44px;
  }

  .side-nav__menu dt a:hover,
  .side-nav__menu dt a:focus {
    border-left-color: transparent;
    border-bottom-color: var(--c-white);
  }

  .side-nav__contact {
    display: none;
  }

  .page-main {
    margin-left: 0;
  }

  .hero {
    min-height: auto;
    padding: 3rem 1.25rem 4rem;
  }

  .hero__title {
    font-size: clamp(1.6rem, 8vw, 2.4rem);
  }

  .wrap {
    padding: 2rem 1.25rem 3rem;
  }

  .site-footer {
    padding: 1.5rem 1.25rem;
  }
}

@media (max-width: 480px) {
  .hero__title {
    font-size: 1.6rem;
  }

  .prose h2 {
    font-size: 1.25rem;
  }

  .side-nav__menu dt a {
    font-size: 0.82rem;
    padding: 0.6rem 0.7rem;
    min-height: 44px;
  }
}