:root {
  --paper: #f7f5ef;
  --panel: #fffdf8;
  --ink: #20211d;
  --muted: #66635a;
  --line: rgba(32, 33, 29, 0.15);
  --soft: #ece6d8;
  --accent: #0f746d;
  --accent-deep: #084c49;
  --red: #a5493f;
  --shadow: 0 16px 44px rgba(45, 38, 24, 0.08);
  --serif: Georgia, "Times New Roman", "Noto Serif SC", serif;
  --sans: ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", "Helvetica Neue", Arial, "Noto Sans SC", sans-serif;
  --mono: "SFMono-Regular", "Cascadia Mono", "Liberation Mono", Menlo, monospace;
}

html[data-theme="dark"] {
  --paper: #101312;
  --panel: #181d1b;
  --ink: #f2eee5;
  --muted: #b9b2a6;
  --line: rgba(242, 238, 229, 0.15);
  --soft: #202721;
  --accent: #5ec7bd;
  --accent-deep: #b6f3ee;
  --red: #ec897d;
  --shadow: 0 20px 60px rgba(0, 0, 0, 0.34);
  color-scheme: dark;
}

* {
  box-sizing: border-box;
}

html {
  max-width: 100%;
  overflow-x: hidden;
  scroll-behavior: smooth;
}

body {
  margin: 0;
  max-width: 100%;
  overflow-x: hidden;
  color: var(--ink);
  font-family: var(--sans);
  line-height: 1.72;
  letter-spacing: 0;
  background:
    linear-gradient(90deg, rgba(32, 33, 29, 0.032) 1px, transparent 1px) 0 0 / 44px 44px,
    linear-gradient(0deg, rgba(32, 33, 29, 0.026) 1px, transparent 1px) 0 0 / 44px 44px,
    var(--paper);
}

html[data-theme="dark"] body {
  background:
    linear-gradient(90deg, rgba(255, 255, 255, 0.04) 1px, transparent 1px) 0 0 / 44px 44px,
    linear-gradient(0deg, rgba(255, 255, 255, 0.032) 1px, transparent 1px) 0 0 / 44px 44px,
    var(--paper);
}

a {
  color: inherit;
}

button {
  font: inherit;
  cursor: pointer;
}

.skip-link {
  position: fixed;
  top: 0.75rem;
  left: 0.75rem;
  z-index: 80;
  width: 1px;
  height: 1px;
  padding: 0.55rem 0.75rem;
  overflow: hidden;
  color: #fff;
  clip: rect(0, 0, 0, 0);
  clip-path: inset(50%);
  text-decoration: none;
  background: var(--ink);
  border-radius: 4px;
}

.skip-link:focus {
  width: auto;
  height: auto;
  overflow: visible;
  clip: auto;
  clip-path: none;
}

.reading-progress {
  position: fixed;
  top: 0;
  left: 0;
  z-index: 100;
  width: 100%;
  height: 3px;
}

.reading-progress span {
  display: block;
  width: 0%;
  height: 100%;
  background: var(--accent);
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  min-height: 58px;
  padding: 0.85rem max(1rem, calc((100vw - 1040px) / 2));
  background: color-mix(in srgb, var(--paper) 94%, transparent);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(14px);
}

.brand,
.module-nav a,
.page-footer a {
  text-decoration: none;
}

.brand {
  font-family: var(--serif);
  font-weight: 800;
}

.module-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
}

.module-nav a,
.page-footer a {
  padding: 0.42rem 0.62rem;
  color: var(--muted);
  font-size: 0.86rem;
  font-weight: 800;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 4px;
}

.module-nav a:hover,
.module-nav a:focus-visible,
.page-footer a:hover,
.page-footer a:focus-visible {
  color: #fff;
  background: var(--accent);
  outline: none;
}

.lecture {
  width: min(100% - 2rem, 940px);
  margin: 0 auto;
  overflow-x: hidden;
  padding: 2rem 0 4rem;
}

.paper-header {
  padding: 3.2rem 0 2rem;
  border-bottom: 3px double var(--line);
}

.kicker {
  margin: 0 0 0.8rem;
  color: var(--accent-deep);
  font-family: var(--mono);
  font-size: 0.78rem;
  font-weight: 850;
  text-transform: uppercase;
}

.paper-header h1 {
  max-width: 880px;
  margin: 0;
  font-family: var(--serif);
  font-size: clamp(2.55rem, 6.6vw, 4.9rem);
  line-height: 1.03;
  letter-spacing: 0;
}

.subtitle {
  max-width: 820px;
  margin: 1.1rem 0 0;
  color: var(--ink);
  font-family: var(--serif);
  font-size: clamp(1.05rem, 2vw, 1.34rem);
  line-height: 1.58;
}

.noscript-note {
  padding: 0.85rem 1rem;
  color: var(--red);
  font-weight: 760;
  background: color-mix(in srgb, var(--red) 9%, transparent);
  border: 1px solid color-mix(in srgb, var(--red) 28%, transparent);
  border-radius: 6px;
}

.chapter {
  padding: 3.4rem 0 0;
}

.chapter-header {
  margin-bottom: 1.2rem;
}

.chapter h2 {
  margin: 0;
  font-family: var(--serif);
  font-size: clamp(1.7rem, 3.4vw, 2.55rem);
  line-height: 1.14;
  letter-spacing: 0;
}

.chapter-summary {
  max-width: 800px;
  margin: 0.65rem 0 0;
  color: var(--muted);
}

.thesis-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 0.75rem;
}

.thesis-grid article,
.answer-note,
.review-grid article {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
}

.thesis-grid article {
  padding: 1rem;
}

.thesis-grid strong {
  display: block;
  margin-bottom: 0.45rem;
  color: var(--accent-deep);
  font-family: var(--serif);
  font-size: 1.08rem;
}

.thesis-grid span {
  color: var(--muted);
}

.section-mount {
  display: grid;
  gap: 0;
}

.answer-list {
  display: grid;
  gap: 1.2rem;
}

.answer-note {
  padding: 1.15rem;
}

.answer-header {
  padding-bottom: 0.9rem;
  margin-bottom: 1rem;
  border-bottom: 1px solid var(--line);
}

.qa-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  margin: 0 0 0.55rem;
}

.qa-meta span {
  padding: 0.16rem 0.45rem;
  color: var(--accent-deep);
  font-size: 0.78rem;
  font-weight: 850;
  background: color-mix(in srgb, var(--accent) 9%, transparent);
  border: 1px solid color-mix(in srgb, var(--accent) 22%, transparent);
  border-radius: 999px;
}

.answer-note h3 {
  margin: 0;
  font-family: var(--serif);
  font-size: clamp(1.2rem, 2vw, 1.55rem);
  line-height: 1.35;
  letter-spacing: 0;
}

.answer-block {
  margin-top: 1.15rem;
}

.answer-block h4 {
  margin: 0 0 0.45rem;
  color: var(--ink);
  font-size: 1rem;
}

.answer-block p,
.answer-block li,
.followup-list p,
.review-grid p {
  color: var(--muted);
}

.answer-block p {
  margin: 0 0 0.72rem;
}

.lead-answer p:first-of-type {
  color: var(--ink);
  font-weight: 780;
}

.formula-stack {
  display: grid;
  gap: 0.55rem;
}

.equation {
  max-width: 100%;
  overflow-x: auto;
  padding: 0.78rem 0.88rem;
  color: var(--ink);
  font-family: var(--mono);
  font-size: 0.92rem;
  background: var(--soft);
  border: 1px solid var(--line);
  border-radius: 6px;
}

.followup-list {
  display: grid;
  gap: 0.65rem;
}

.followup-list article {
  padding: 0.78rem 0.88rem;
  background: color-mix(in srgb, var(--panel) 78%, var(--soft));
  border: 1px solid var(--line);
  border-radius: 6px;
}

.followup-list h4 {
  margin: 0 0 0.35rem;
  font-size: 0.98rem;
}

.memory-hook {
  margin: 1.15rem 0 0;
  padding: 0.72rem 0.85rem;
  color: var(--accent-deep);
  font-weight: 780;
  background: color-mix(in srgb, var(--accent) 9%, transparent);
  border-left: 4px solid var(--accent);
  border-radius: 4px;
}

.review-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.85rem;
}

.review-grid article {
  padding: 1rem;
}

.review-grid h3 {
  margin: 0 0 0.45rem;
  font-family: var(--serif);
}

.page-footer {
  display: flex;
  justify-content: center;
  gap: 0.65rem;
  padding: 2rem 1rem 3rem;
}

.back-to-top,
.toc-toggle {
  position: fixed;
  z-index: 60;
  min-height: 38px;
  padding: 0.55rem 0.72rem;
  color: var(--ink);
  font-weight: 800;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 6px;
}

.back-to-top {
  right: 1rem;
  bottom: 1rem;
  opacity: 0;
  pointer-events: none;
  transition: opacity 160ms ease;
}

.back-to-top.visible {
  opacity: 1;
  pointer-events: auto;
}

.toc-toggle {
  left: 1rem;
  bottom: 1rem;
}

.lecture-toc {
  position: fixed;
  left: 1rem;
  bottom: 4.4rem;
  z-index: 55;
  display: none;
  width: min(22rem, calc(100vw - 2rem));
  max-height: min(32rem, calc(100vh - 7rem));
  overflow: auto;
  padding: 1rem;
  background: color-mix(in srgb, var(--panel) 96%, transparent);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
  backdrop-filter: blur(14px);
}

.lecture-toc.open {
  display: block;
}

.lecture-toc p {
  margin: 0 0 0.75rem;
  color: var(--accent-deep);
  font-family: var(--mono);
  font-size: 0.78rem;
  font-weight: 850;
}

.lecture-toc nav {
  display: grid;
  gap: 0.25rem;
}

.lecture-toc a {
  display: grid;
  gap: 0.12rem;
  padding: 0.42rem 0.5rem;
  color: var(--muted);
  text-decoration: none;
  border-radius: 5px;
}

.lecture-toc a small {
  color: inherit;
  opacity: 0.75;
}

.lecture-toc a.active,
.lecture-toc a:hover,
.lecture-toc a:focus-visible,
.back-to-top:hover,
.back-to-top:focus-visible,
.toc-toggle:hover,
.toc-toggle:focus-visible {
  color: #fff;
  background: var(--accent);
  outline: none;
}

@media (min-width: 1540px) {
  .toc-toggle {
    display: none;
  }

  .lecture-toc {
    top: 5rem;
    bottom: auto;
    left: max(1rem, calc((100vw - 940px) / 2 - 260px));
    display: block;
    width: 13.75rem;
    max-height: calc(100vh - 6rem);
  }
}

@media (max-width: 900px) {
  .thesis-grid,
  .review-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 680px) {
  .site-header {
    align-items: flex-start;
    flex-direction: column;
  }

  .lecture {
    width: min(100% - 1.1rem, 940px);
    padding-top: 1rem;
  }

  .paper-header {
    padding-top: 2rem;
  }

  .thesis-grid,
  .review-grid {
    grid-template-columns: 1fr;
  }
}

@media print {
  .site-header,
  .lecture-toc,
  .toc-toggle,
  .back-to-top {
    display: none !important;
  }

  body {
    background: #fff;
  }

  .lecture {
    width: 100%;
  }

  .answer-note {
    break-inside: avoid;
    box-shadow: none;
  }
}