:root {
  --ink: #17202b;
  --muted: #5c6672;
  --paper: #fbfaf6;
  --accent: #9e3b32;
  --line: #ded9cf;
}

body {
  color: var(--ink);
  background: var(--paper);
  font-family: "Noto Serif SC", "Source Han Serif SC", "Songti SC", SimSun, serif;
  font-size: 1.06rem;
  line-height: 1.88;
}

.content p {
  margin-top: 0.9rem;
  margin-bottom: 0.9rem;
}

h1, h2, h3 {
  color: #16202c;
  letter-spacing: 0.01em;
}

h1 {
  font-weight: 750;
  line-height: 1.35;
}

h2 {
  margin-top: 2.4rem;
  padding-bottom: 0.28rem;
  border-bottom: 1px solid var(--line);
}

h3 {
  margin-top: 1.9rem;
}

blockquote {
  color: #3f4954;
  background: #f2efe8;
  border-left: 4px solid #707b86;
  padding: 0.8rem 1.1rem;
}

strong {
  color: #17202b;
}

a {
  color: #7f302a;
}

code {
  color: #6f2c27;
}

.sidebar-title {
  font-family: "Noto Serif SC", "Source Han Serif SC", "Songti SC", SimSun, serif;
}

/*
 * Reading grid
 * Keep the book navigation visible without allowing the two side columns to
 * squeeze the lesson into a narrow strip. The right-hand chapter outline is
 * useful on a large monitor; on a laptop or tablet, the text deserves the room.
 */
main.content {
  width: 100%;
  max-width: none;
  min-width: 0;
}

@media (min-width: 992px) and (max-width: 1239.98px) {
  body.docked #quarto-content.page-columns {
    grid-template-columns:
      [screen-start] 1.25rem
      [screen-start-inset page-start] minmax(76px, 96px)
      [page-start-inset] 40px
      [body-start-outset] 40px
      [body-start] 1.25rem
      [body-content-start] minmax(0, 1fr)
      [body-content-end] 1.25rem
      [body-end body-end-outset page-end-inset page-end] minmax(1.25rem, 0.12fr)
      [screen-end-inset] 1.25rem
      [screen-end];
  }
}

@media (max-width: 1239.98px) {
  #quarto-margin-sidebar {
    display: none;
  }
}

@media (max-width: 991.98px) {
  body #quarto-content.page-columns {
    grid-template-columns:
      [screen-start screen-start-inset page-start page-start-inset body-start-outset body-start] 1.1rem
      [body-content-start] minmax(0, 1fr)
      [body-content-end] 1.1rem
      [body-end body-end-outset page-end-inset page-end screen-end-inset screen-end];
  }
}

.interactive-block {
  margin: 1.4rem 0 2rem;
  padding: 0.85rem;
  background: #f1eee7;
  border: 1px solid var(--line);
  border-radius: 14px;
}

.interactive-block iframe {
  display: block;
  width: 100%;
  border: 0;
  border-radius: 10px;
  background: #101820;
  box-shadow: 0 12px 32px rgba(21, 29, 38, 0.12);
}

.interactive-block .interactive-caption {
  margin: 0.7rem 0 0;
  color: var(--muted);
  font-size: 0.88rem;
  line-height: 1.6;
}

.interactive-block .interactive-caption a {
  white-space: nowrap;
}

.advanced-case {
  margin: 1rem 0 1.8rem;
  border: 1px solid #d7cfc1;
  border-radius: 11px;
  background: #f6f3ec;
}

.advanced-case > summary {
  padding: 0.78rem 0.9rem;
  color: #6d4328;
  font-family: "Microsoft YaHei", "Noto Sans SC", sans-serif;
  font-size: 0.86rem;
  font-weight: 650;
  cursor: pointer;
}

.advanced-case > .interactive-block {
  margin: 0;
  border: 0;
  border-top: 1px solid #ddd5c8;
  border-radius: 0 0 11px 11px;
}

.real-bridge-figure {
  margin: 1.5rem 0 2rem;
  padding: 0.55rem;
  background: #f1eee7;
  border: 1px solid var(--line);
  border-radius: 12px;
}

.real-bridge-figure img {
  display: block;
  width: 100%;
  max-height: 560px;
  object-fit: cover;
  border-radius: 8px;
}

.real-bridge-figure p {
  margin: 0.65rem 0.25rem 0.15rem;
  color: var(--muted);
  font-family: "Microsoft YaHei", "Segoe UI", sans-serif;
  font-size: 0.86rem;
  line-height: 1.65;
}

.chapter-question {
  margin: 0.8rem 0 1.55rem;
  padding: 0.9rem 1.05rem 1rem;
  color: #20313a;
  background: linear-gradient(135deg, #f3f8f8 0%, #fffaf0 100%);
  border: 1px solid #d6e1e1;
  border-left: 5px solid #1f8fa8;
  border-radius: 0 10px 10px 0;
}

.chapter-question p {
  margin: 0;
  font-family: "Noto Serif SC", "Source Han Serif SC", "Songti SC", SimSun, serif;
  font-size: 1.08rem;
  line-height: 1.72;
}

.chapter-question::before,
.editor-extension::before {
  display: block;
  margin-bottom: 0.35rem;
  color: #8a5a2a;
  font-family: "Microsoft YaHei", "Segoe UI", sans-serif;
  font-size: 0.72rem;
  letter-spacing: 0.08em;
}

.chapter-question::before {
  content: attr(data-term);
  width: fit-content;
  margin-bottom: 0.5rem;
  padding: 0.16rem 0.5rem;
  color: #0f6174;
  background: #e3f3f5;
  border-radius: 999px;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.04em;
}

.chapter-method {
  margin: 1.55rem 0 1.1rem;
  padding: 0.85rem 1rem;
  color: #30434c;
  background: #f5f8f7;
  border-top: 1px solid #cad9d6;
  border-bottom: 1px solid #cad9d6;
}

.chapter-method::before {
  content: "这一章，带走一招";
  display: block;
  margin-bottom: 0.35rem;
  color: #24705f;
  font-family: "Microsoft YaHei", "Segoe UI", sans-serif;
  font-size: 0.76rem;
  font-weight: 700;
  letter-spacing: 0.06em;
}

.chapter-method p {
  margin: 0;
  line-height: 1.72;
}

.editor-extension {
  margin: 1.2rem 0;
  padding: 0.15rem 0 0.15rem 1rem;
  color: #44505a;
  border-left: 2px solid #b9a98f;
}

.editor-extension::before {
  content: "编者延伸";
  color: #75654f;
}

.editor-extension p {
  margin: 0;
}

@media (max-width: 700px) {
  .interactive-block {
    margin-left: -0.6rem;
    margin-right: -0.6rem;
    padding: 0.5rem;
  }
}

/* 小节闪卡：一次只做一次提取，解释按需展开。 */
.section-flashcards {
  --card-ink: #1b3037;
  --card-muted: #617078;
  --card-line: #d5dfdf;
  --card-paper: #f7f9f8;
  --card-copper: #b95f35;
  --card-teal: #245d67;
  width: 100%;
  min-width: 0;
  margin: 0.78rem 0 1.35rem;
  color: var(--card-ink);
  font-family: "Microsoft YaHei", "Noto Sans SC", sans-serif;
}

.section-flashcards [hidden] {
  display: none !important;
}

.section-flashcards button {
  min-height: 44px;
  margin: 0;
  font: inherit;
  cursor: pointer;
  touch-action: manipulation;
}

.section-flashcards button:focus-visible,
.section-flashcard__why > summary:focus-visible {
  outline: 3px solid rgba(36, 93, 103, 0.28);
  outline-offset: 2px;
}

.section-flashcards__toolbar {
  display: flex;
  gap: 0.7rem;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 0.42rem;
}

.section-flashcards__modes {
  display: inline-flex;
  padding: 2px;
  background: #edf2f1;
  border: 1px solid var(--card-line);
  border-radius: 7px;
}

.section-flashcards__mode {
  padding: 0.35rem 0.72rem;
  color: #5c6b71;
  background: transparent;
  border: 0;
  border-radius: 5px;
  font-size: 0.75rem !important;
  font-weight: 650 !important;
}

.section-flashcards__mode.is-active {
  color: #fff;
  background: var(--card-teal);
  box-shadow: 0 1px 3px rgba(20, 47, 54, 0.18);
}

.section-flashcards__device-note {
  color: #7a878c;
  font-size: 0.66rem;
}

.section-flashcards__stage {
  min-width: 0;
}

.section-flashcard {
  position: relative;
  min-width: 0;
  overflow: hidden;
  background: var(--card-paper);
  border: 1px solid var(--card-line);
  border-left: 4px solid var(--card-copper);
  border-radius: 9px;
  box-shadow: 0 7px 20px rgba(29, 50, 57, 0.06);
}

.section-flashcard::before {
  position: absolute;
  top: 0;
  right: 0;
  left: 0;
  height: 3px;
  background: var(--card-teal);
  content: "";
  opacity: 0.88;
}

.section-flashcard__meta {
  display: flex;
  gap: 0.75rem;
  align-items: center;
  justify-content: space-between;
  min-width: 0;
  padding: 0.72rem 0.9rem 0;
  color: var(--card-muted);
  font-size: 0.69rem;
  font-weight: 700;
  letter-spacing: 0.025em;
}

.section-flashcard__principle {
  min-width: 0;
  padding-left: 0.48rem;
  overflow-wrap: anywhere;
  border-left: 2px solid #d58b5e;
  color: #87431f;
}

.section-flashcard__count {
  flex: none;
  color: #5f6f75;
  font-variant-numeric: tabular-nums;
}

.section-flashcard__face {
  min-width: 0;
  padding: 0.86rem 0.92rem 0.72rem;
}

.section-flashcard__front {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 0.8rem;
  align-items: end;
  min-height: 8.4rem;
}

.section-flashcard__question {
  max-width: 35em;
  margin: 0;
  overflow-wrap: anywhere;
  color: var(--card-ink);
  font-family: "Noto Serif SC", "Source Han Serif SC", "Songti SC", SimSun, serif;
  font-size: clamp(1.02rem, 1.6vw, 1.18rem);
  font-weight: 650;
  line-height: 1.66;
}

.section-flashcard__reveal {
  align-self: end;
  padding: 0.42rem 0.86rem;
  color: #fff;
  background: var(--card-teal);
  border: 1px solid var(--card-teal);
  border-radius: 6px;
  font-size: 0.77rem !important;
  font-weight: 700 !important;
  white-space: nowrap;
}

.section-flashcard__back {
  min-height: 8.4rem;
}

.section-flashcard__short-answer {
  max-width: 45em;
  margin: 0;
  overflow-wrap: anywhere;
  color: #263b42;
  font-size: 0.91rem;
  font-weight: 550;
  line-height: 1.75;
}

.section-flashcard__why {
  margin-top: 0.66rem;
  border-top: 1px solid var(--card-line);
}

.section-flashcard__why > summary {
  display: inline-flex;
  align-items: center;
  min-height: 44px;
  padding: 0.2rem 0;
  color: var(--card-teal);
  cursor: pointer;
  font-size: 0.76rem;
  font-weight: 750;
  list-style: none;
}

.section-flashcard__why > summary::-webkit-details-marker {
  display: none;
}

.section-flashcard__why > summary::after {
  margin-left: 0.35rem;
  content: "+";
  font-size: 0.95rem;
}

.section-flashcard__why[open] > summary::after {
  content: "−";
}

.section-flashcard__why dl {
  display: grid;
  gap: 0.48rem;
  margin: 0 0 0.72rem;
}

.section-flashcard__detail-row {
  display: grid;
  grid-template-columns: 3.1rem minmax(0, 1fr);
  gap: 0.55rem;
  padding-left: 0.62rem;
  border-left: 2px solid #cad8d7;
}

.section-flashcard__detail-row dt,
.section-flashcard__detail-row dd {
  margin: 0;
  overflow-wrap: anywhere;
  font-size: 0.73rem;
  line-height: 1.62;
}

.section-flashcard__detail-row dt {
  color: #7b492f;
  font-weight: 750;
}

.section-flashcard__detail-row dd {
  color: #5b696f;
}

.section-flashcard__ratings {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.58rem;
  margin-top: 0.72rem;
}

.section-flashcard__rating {
  padding: 0.42rem 0.7rem;
  border: 1px solid #bdc9c9;
  border-radius: 6px;
  font-size: 0.76rem !important;
  font-weight: 700 !important;
}

.section-flashcard__rating--missed {
  color: #78432d;
  background: #fffaf6;
}

.section-flashcard__rating--clear {
  color: #22594e;
  background: #f5fbf8;
}

.section-flashcard__rating--missed.is-selected {
  background: #f5e4da;
  border-color: #c88460;
}

.section-flashcard__rating--clear.is-selected {
  background: #dfeee8;
  border-color: #6c9e8d;
}

.section-flashcard__navigation {
  display: flex;
  gap: 0.35rem;
  justify-content: flex-end;
  padding: 0 0.72rem 0.65rem;
}

.section-flashcard__nav {
  display: inline-grid;
  width: 44px;
  min-width: 44px;
  padding: 0;
  place-items: center;
  color: var(--card-teal);
  background: transparent;
  border: 1px solid #c8d4d4;
  border-radius: 6px;
  font-size: 1rem !important;
}

.section-flashcard__nav:disabled {
  cursor: default;
  opacity: 0.34;
}

.section-flashcards__progress {
  height: 3px;
  margin: 0.36rem 5px 0;
  overflow: hidden;
  background: #e2e9e8;
  border-radius: 0;
}

.section-flashcards__progress > span {
  display: block;
  width: 0;
  height: 100%;
  background: var(--card-copper);
  transition: width 180ms ease;
}

.section-flashcards__finish {
  padding: 1.05rem;
  background: #f5f8f7;
  border: 1px solid var(--card-line);
  border-left: 4px solid var(--card-teal);
  border-radius: 9px;
}

.section-flashcards__finish-title,
.section-flashcards__finish-counts {
  margin: 0;
}

.section-flashcards__finish-title {
  color: var(--card-ink);
  font-family: "Noto Serif SC", "Source Han Serif SC", "Songti SC", SimSun, serif;
  font-size: 1rem;
  font-weight: 700;
}

.section-flashcards__finish-counts {
  margin-top: 0.25rem;
  color: var(--card-muted);
  font-size: 0.75rem;
}

.section-flashcards__finish-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
  margin-top: 0.8rem;
}

.section-flashcards__retry {
  padding: 0.42rem 0.82rem;
  color: var(--card-teal);
  background: transparent;
  border: 1px solid #9eb5b7;
  border-radius: 6px;
  font-size: 0.75rem !important;
  font-weight: 700 !important;
}

.section-flashcards__retry--primary {
  color: #fff;
  background: var(--card-teal);
  border-color: var(--card-teal);
}

@media (max-width: 700px) {
  .section-flashcards {
    margin-top: 0.65rem;
  }

  .section-flashcards__toolbar {
    align-items: flex-start;
  }

  .section-flashcards__device-note {
    max-width: 8rem;
    padding-top: 0.24rem;
    text-align: right;
  }

  .section-flashcard__meta {
    padding-right: 0.7rem;
    padding-left: 0.7rem;
  }

  .section-flashcard__face {
    padding-right: 0.72rem;
    padding-left: 0.72rem;
  }

  .section-flashcard__front {
    grid-template-columns: 1fr;
    min-height: 0;
  }

  .section-flashcard__reveal {
    width: 100%;
  }

  .section-flashcard__ratings {
    grid-template-columns: 1fr;
  }

  .section-flashcard__detail-row {
    grid-template-columns: 2.7rem minmax(0, 1fr);
    gap: 0.42rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  .section-flashcards__progress > span {
    transition: none;
  }
}

.reading-tools-link {
  margin: 1.35rem 0 1.7rem;
  border-left: 4px solid #d88b24;
  padding: 0.85rem 1rem;
  background: #fff5df;
  color: #243d45;
}

.reading-tools-link p:last-child {
  margin-bottom: 0;
}

.manim-film {
  width: min(100%, 58rem);
  margin: 1.25rem auto 1.55rem;
  border: 1px solid #cbd7d7;
  border-radius: 0.75rem;
  overflow: hidden;
  background: #f4f0e6;
  box-shadow: 0 18px 42px rgba(16, 42, 54, 0.09);
}

.manim-film video {
  display: block;
  width: 100%;
  aspect-ratio: 16 / 9;
  background: #f4f0e6;
}

.manim-film p {
  margin: 0;
  border-top: 1px solid #d8e0df;
  padding: 0.65rem 0.85rem;
  color: #61747d;
  font-size: 0.82rem;
  line-height: 1.6;
}

.manim-actions,
.figure-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  border-top: 1px solid #d8e0df;
  padding: 0.65rem 0.85rem 0.8rem;
  background: rgba(255, 255, 255, 0.72);
}

.manim-actions a,
.figure-actions a {
  display: inline-flex;
  min-height: 2.5rem;
  align-items: center;
  border: 1px solid #9fb3b9;
  border-radius: 999px;
  padding: 0.42rem 0.78rem;
  color: #17313b;
  background: #fff;
  font-size: 0.76rem;
  font-weight: 700;
  text-decoration: none;
}

.manim-actions a:hover,
.manim-actions a:focus-visible,
.figure-actions a:hover,
.figure-actions a:focus-visible {
  border-color: #197f96;
  background: #dceff2;
}

.data-figure {
  width: min(100%, 58rem);
  margin: 1.1rem auto 1.6rem;
  border: 1px solid #cbd7d7;
  border-radius: 0.75rem;
  overflow: hidden;
  background: #fff;
  box-shadow: 0 14px 34px rgba(16, 42, 54, 0.07);
}

.data-figure img {
  display: block;
  width: 100%;
  height: auto;
  background: #f8f6ef;
}

.data-figure figcaption {
  border-top: 1px solid #d8e0df;
  padding: 0.7rem 0.9rem;
  color: #536b74;
  font-size: 0.82rem;
  line-height: 1.65;
}

.math-step {
  margin: 0.8rem 0 1rem;
  border: 1px solid #cbd7d7;
  border-radius: 0.55rem;
  padding: 0.65rem 0.85rem;
  background: rgba(255, 255, 255, 0.68);
}

.math-step summary {
  min-height: 2.2rem;
  cursor: pointer;
  color: #197f96;
  font-weight: 700;
}

.story-shelf {
  margin: 1rem 0 1.2rem;
  border-left: 4px solid #d88b24;
  padding: 0.75rem 0.9rem;
  background: #fff7e7;
}

.story-shelf summary {
  min-height: 2.2rem;
  cursor: pointer;
  color: #725324;
  font-weight: 700;
}

@media (max-width: 640px) {
  .manim-film {
    border-radius: 0.45rem;
  }
}

/* Independent experience page: show the work quietly, through usable examples. */
.experience-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
  margin: 1.35rem 0 1.75rem;
}

/* Pandoc wraps raw anchor blocks in paragraphs; let the anchors remain grid items. */
.experience-grid > p {
  display: contents;
}

.experience-card {
  position: relative;
  display: grid;
  grid-template-rows: minmax(12rem, 1fr) auto;
  min-width: 0;
  overflow: hidden;
  border: 1px solid #ccd9db;
  border-radius: 0.85rem;
  color: #17313b;
  background: #f8f6ef;
  box-shadow: 0 14px 36px rgba(20, 48, 60, 0.08);
  text-decoration: none;
  transition: transform 180ms ease, border-color 180ms ease, box-shadow 180ms ease;
}

.experience-card:hover,
.experience-card:focus-visible {
  transform: translateY(-3px);
  border-color: #328a9b;
  color: #17313b;
  box-shadow: 0 20px 42px rgba(20, 48, 60, 0.14);
  text-decoration: none;
}

.experience-card--wide {
  grid-column: span 2;
  grid-template-columns: minmax(0, 1.35fr) minmax(16rem, 0.65fr);
  grid-template-rows: minmax(16rem, 20rem);
}

.experience-card img {
  width: 100%;
  height: 100%;
  min-height: 12rem;
  object-fit: contain;
  object-position: center;
  background: #e7edef;
}

.experience-card__body {
  display: flex;
  min-width: 0;
  flex-direction: column;
  justify-content: center;
  gap: 0.48rem;
  padding: 1rem 1.05rem 1.1rem;
}

.experience-card__term {
  align-self: flex-start;
  border-radius: 999px;
  padding: 0.24rem 0.58rem;
  color: #176c7e;
  background: #dceef1;
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.04em;
}

.experience-card strong {
  font-family: "Noto Serif SC", "Source Han Serif SC", Georgia, serif;
  font-size: clamp(1.02rem, 1.4vw, 1.3rem);
  line-height: 1.48;
}

.experience-card__body > span:last-child {
  color: #60747c;
  font-size: 0.86rem;
  line-height: 1.6;
}

@media (max-width: 760px) {
  .experience-grid {
    grid-template-columns: 1fr;
  }

  .experience-card,
  .experience-card--wide {
    grid-column: auto;
    grid-template-columns: 1fr;
    grid-template-rows: 12rem auto;
  }

  .experience-card strong {
    font-size: 1.02rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  .experience-card {
    transition: none;
  }
}

.worked-question,
.worked-example-link {
  margin: 1rem 0 1.3rem;
  border-left: 4px solid #197f96;
  padding: 0.85rem 1rem;
  color: #243d45;
  background: #eaf4f5;
}

.worked-question p:last-child,
.worked-example-link p:last-child {
  margin-bottom: 0;
}

.case-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
  margin: 1rem 0 1.45rem;
}

.case-actions .btn {
  display: inline-flex;
  min-height: 2.65rem;
  align-items: center;
}

.pdf-preview {
  margin: 1.25rem 0 1.6rem;
  overflow: hidden;
  border: 1px solid #cbd7d7;
  border-radius: 0.7rem;
  background: #fff;
}

.pdf-preview summary {
  cursor: pointer;
  padding: 0.8rem 1rem;
  color: #176c7e;
  background: #eef5f5;
  font-weight: 800;
}

.pdf-preview object {
  display: block;
  border: 0;
  border-top: 1px solid #d7e0e1;
}

@media (max-width: 640px) {
  .pdf-preview object {
    height: 62vh;
  }
}
.external-workbench {
  margin: 1rem 0 1.35rem;
  border: 1px solid #d6e1e3;
  border-radius: 16px;
  overflow: hidden;
  background: #fff;
  box-shadow: 0 14px 34px rgba(16, 42, 54, 0.09);
}

.external-workbench iframe {
  display: block;
  width: 100%;
  min-height: 680px;
  border: 0;
  background: #eef3f4;
}

.external-workbench .interactive-caption {
  margin: 0;
  padding: 0.8rem 1rem 0.95rem;
}

@media (max-width: 720px) {
  .external-workbench iframe {
    min-height: 720px;
  }
}