/* =========================================================
   GOWEB — 중간고사 정리
   Editorial study guide. Paper, ink, cobalt.
   ========================================================= */

@import url("https://cdn.jsdelivr.net/gh/orioncactus/pretendard@v1.3.9/dist/web/variable/pretendardvariable-dynamic-subset.min.css");

:root {
  --paper: #f4f0e6;
  --paper-raised: #fbf8f1;
  --paper-deep: #ebe5d7;
  --ink: #17170f;
  --ink-soft: #45443a;
  --muted: #6f6c60;
  --line: #d8d1c0;
  --line-strong: #b9b09b;
  --blue: #1e46d6;
  --blue-dark: #1636a8;
  --blue-soft: #e6eafa;
  --red: #b33a24;
  --red-soft: #f7e8e2;
  --green: #1f6b4f;
  --green-soft: #e4efe9;
  --sans: "Pretendard Variable", Pretendard, -apple-system, BlinkMacSystemFont,
    "Apple SD Gothic Neo", "Noto Sans KR", sans-serif;
  --display: var(--sans);
  --mono: var(--sans);
  --shell: 1200px;
  --header-h: 66px;
  --radius: 4px;
  --shadow: 0 1px 0 rgba(23, 23, 15, 0.04), 0 18px 50px -32px rgba(23, 23, 15, 0.28);
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + 28px);
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16.5px;
  line-height: 1.72;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  word-break: keep-all;
}

::selection {
  background: var(--blue);
  color: #fff;
}

a {
  color: inherit;
  text-decoration: none;
}

button {
  font: inherit;
  color: inherit;
}

img,
svg {
  display: block;
  max-width: 100%;
}

h1,
h2,
h3,
h4,
p,
ul,
ol,
dl,
dd,
figure {
  margin: 0;
}

ul,
ol {
  padding: 0;
  list-style: none;
}

:focus-visible {
  outline: 2px solid var(--blue);
  outline-offset: 3px;
}

.skip {
  position: fixed;
  top: -100px;
  left: 16px;
  z-index: 200;
  padding: 10px 16px;
  background: var(--ink);
  color: var(--paper);
  font-family: var(--mono);
  font-size: 13px;
}

.skip:focus {
  top: 12px;
}

.shell {
  width: 100%;
  max-width: var(--shell);
  margin: 0 auto;
  padding: 0 36px;
}

/* ---------- header ---------- */

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-h);
  border-bottom: 1px solid var(--line);
  background: rgba(244, 240, 230, 0.92);
  background: color-mix(in srgb, var(--paper) 92%, transparent);
  backdrop-filter: blur(12px);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  gap: 24px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 11px;
  flex: none;
}

.brand-mark {
  display: grid;
  place-items: center;
  width: 31px;
  height: 31px;
  border: 1.5px solid var(--ink);
  font-family: var(--display);
  font-size: 19px;
  line-height: 1;
  transition: background 0.2s, color 0.2s;
}

.brand:hover .brand-mark {
  background: var(--ink);
  color: var(--paper);
}

.brand-text {
  display: flex;
  flex-direction: column;
  line-height: 1.15;
}

.brand-text strong {
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.16em;
}

.brand-text small {
  margin-top: 3px;
  color: var(--muted);
  font-size: 11.5px;
  letter-spacing: 0.02em;
}

.top-nav {
  display: flex;
  align-items: center;
  gap: 26px;
  font-size: 13.5px;
  font-weight: 500;
}

.top-nav > a {
  position: relative;
  padding: 4px 0;
  color: var(--ink-soft);
}

.top-nav > a:hover {
  color: var(--ink);
}

.top-nav > a::after {
  content: "";
  position: absolute;
  left: 0;
  right: 100%;
  bottom: 0;
  height: 1px;
  background: var(--ink);
  transition: right 0.22s ease;
}

.top-nav > a:hover::after {
  right: 0;
}

.nav-cheat {
  padding: 7px 13px !important;
  border: 1px solid var(--ink);
  color: var(--ink) !important;
  transition: background 0.18s, color 0.18s;
}

.nav-cheat::after {
  display: none;
}

.nav-cheat:hover {
  background: var(--ink);
  color: var(--paper) !important;
}

.search-trigger {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 9px 6px 11px;
  border: 1px solid var(--line-strong);
  border-radius: 999px;
  background: transparent;
  color: var(--muted);
  font-size: 13.5px;
  cursor: pointer;
  transition: border-color 0.18s, color 0.18s;
}

.search-trigger:hover {
  border-color: var(--ink);
  color: var(--ink);
}

.search-trigger kbd {
  display: inline-grid;
  place-items: center;
  min-width: 19px;
  height: 19px;
  padding: 0 4px;
  border: 1px solid var(--line);
  border-radius: 3px;
  background: var(--paper-raised);
  font-family: var(--mono);
  font-size: 11.5px;
}

.progress {
  position: absolute;
  left: 0;
  bottom: -1px;
  width: 0;
  height: 2px;
  background: var(--blue);
  transition: width 0.08s linear;
}

/* ---------- shared type ---------- */

.kicker {
  display: flex;
  align-items: center;
  gap: 10px;
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 500;
  letter-spacing: 0.14em;
  line-height: 1.4;
  text-transform: uppercase;
  color: var(--muted);
}

.kicker-line {
  display: inline-block;
  width: 28px;
  height: 1px;
  background: var(--blue);
}

.section-head {
  display: grid;
  grid-template-columns: 1fr;
  gap: 9px;
  margin-bottom: 30px;
}

.section-head h2 {
  font-family: var(--display);
  font-size: clamp(27px, 3vw, 36px);
  font-weight: 700;
  line-height: 1.28;
  letter-spacing: -0.025em;
}

.section-head p:not(.kicker) {
  max-width: 560px;
  color: var(--muted);
  font-size: 14.5px;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  min-height: 46px;
  padding: 0 20px;
  border: 1px solid var(--ink);
  font-size: 14px;
  font-weight: 600;
  letter-spacing: -0.01em;
  transition: transform 0.18s ease, background 0.18s ease, color 0.18s ease;
}

.btn:hover {
  transform: translateY(-2px);
}

.btn-primary {
  background: var(--ink);
  color: var(--paper);
}

.btn-primary:hover {
  background: var(--blue);
  border-color: var(--blue);
}

.btn-ghost {
  background: transparent;
  color: var(--ink);
}

.btn-ghost:hover {
  background: var(--paper-raised);
}

.btn .arrow {
  font-family: var(--mono);
  font-weight: 400;
}

/* ---------- hero ---------- */

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 310px;
  align-items: end;
  gap: 70px;
  padding-top: 92px;
  padding-bottom: 76px;
}

.hero h1 {
  margin-top: 22px;
  font-family: var(--display);
  font-size: clamp(46px, 5.8vw, 74px);
  font-weight: 700;
  line-height: 1.12;
  letter-spacing: -0.045em;
}

.hero h1 em {
  position: relative;
  font-style: normal;
  color: var(--blue);
}

.hero-lede {
  max-width: 590px;
  margin-top: 25px;
  color: var(--ink-soft);
  font-size: 17.5px;
  line-height: 1.75;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 11px;
  margin-top: 32px;
}

.hero-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0;
  margin-top: 40px;
  border-top: 1px solid var(--line);
  padding-top: 15px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 11.5px;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.hero-meta span {
  display: inline-flex;
  align-items: center;
  gap: 8px;
}

.hero-meta span + span::before {
  content: "";
  display: inline-block;
  width: 3px;
  height: 3px;
  margin: 0 14px;
  border-radius: 50%;
  background: var(--line-strong);
}

.exam-card {
  position: relative;
  isolation: isolate;
  border: 1px solid var(--ink);
  background: var(--paper-raised);
  box-shadow: var(--shadow);
}

.exam-card::before {
  content: "";
  position: absolute;
  top: 7px;
  left: 7px;
  right: -7px;
  bottom: -7px;
  border-right: 1px solid var(--line-strong);
  border-bottom: 1px solid var(--line-strong);
  z-index: -1;
}

.exam-card-head {
  display: flex;
  justify-content: space-between;
  padding: 12px 16px;
  border-bottom: 1px solid var(--ink);
  background: var(--ink);
  color: var(--paper);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.15em;
}

.exam-card-body {
  padding: 20px 16px 18px;
}

.exam-card-label {
  margin-bottom: 13px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.exam-card ol {
  display: grid;
  gap: 13px;
}

.exam-card li {
  display: grid;
  grid-template-columns: 54px 1fr;
  gap: 10px;
  padding-bottom: 13px;
  border-bottom: 1px dashed var(--line);
  font-size: 13.5px;
  line-height: 1.5;
}

.exam-card li:last-child {
  padding-bottom: 0;
  border-bottom: 0;
}

.exam-card li b {
  font-family: var(--display);
  font-size: 14px;
  font-weight: 700;
}

.exam-card li span {
  color: var(--muted);
  font-size: 12.5px;
}

.exam-card-foot {
  display: flex;
  justify-content: space-between;
  padding: 11px 16px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.12em;
}

.exam-card-foot b {
  color: var(--ink);
  font-weight: 600;
}

/* ---------- spine ---------- */

.spine-section {
  padding-top: 58px;
  padding-bottom: 78px;
  border-top: 1px solid var(--line);
}

.spine {
  position: relative;
  display: grid;
  grid-template-columns: repeat(7, 1fr);
  gap: 0;
  margin-top: 38px;
}

.spine::before {
  content: "";
  position: absolute;
  top: 15px;
  left: 7%;
  right: 7%;
  height: 1px;
  background: var(--line-strong);
}

.spine li {
  position: relative;
  padding-right: 14px;
}

.spine-dot {
  position: relative;
  z-index: 1;
  display: grid;
  place-items: center;
  width: 31px;
  height: 31px;
  margin-bottom: 18px;
  border: 1px solid var(--line-strong);
  border-radius: 50%;
  background: var(--paper);
  font-family: var(--mono);
  font-size: 11px;
  color: var(--muted);
  transition: background 0.2s, color 0.2s, border-color 0.2s;
}

.spine li:hover .spine-dot {
  background: var(--blue);
  border-color: var(--blue);
  color: #fff;
}

.spine-label {
  display: block;
  margin-bottom: 5px;
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.08em;
  color: var(--muted);
  text-transform: uppercase;
}

.spine-title {
  display: block;
  max-width: 130px;
  font-size: 13.5px;
  font-weight: 600;
  line-height: 1.45;
  letter-spacing: -0.02em;
}

/* ---------- chapter index ---------- */

.chapters {
  padding-top: 62px;
  padding-bottom: 92px;
  border-top: 1px solid var(--line);
}

.chapter-list {
  border-top: 1px solid var(--ink);
}

.chapter-row {
  display: grid;
  grid-template-columns: 64px minmax(0, 1fr) 250px 32px;
  align-items: center;
  gap: 24px;
  padding: 23px 10px 23px 4px;
  border-bottom: 1px solid var(--line);
  transition: background 0.2s ease, padding 0.2s ease;
}

.chapter-row:hover {
  padding-left: 14px;
  background: var(--paper-raised);
}

.chapter-num {
  font-family: var(--mono);
  font-size: 13px;
  color: var(--blue);
  letter-spacing: 0.04em;
}

.chapter-main {
  display: flex;
  flex-direction: column;
  gap: 3px;
}

.chapter-main strong {
  font-family: var(--display);
  font-size: 23px;
  font-weight: 700;
  line-height: 1.35;
  letter-spacing: -0.025em;
}

.chapter-main small {
  color: var(--muted);
  font-size: 14px;
  line-height: 1.5;
}

.chapter-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 5px;
}

.chapter-tags span {
  padding: 3px 7px;
  border: 1px solid var(--line);
  color: var(--muted);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.01em;
  white-space: nowrap;
}

.chapter-arrow {
  font-size: 19px;
  color: var(--muted);
  text-align: right;
  transition: color 0.2s, transform 0.2s;
}

.chapter-row:hover .chapter-arrow {
  color: var(--blue);
  transform: translate(2px, -2px);
}

/* ---------- chapter hero ---------- */

.chapter-hero {
  position: relative;
  overflow: hidden;
  border-bottom: 1px solid var(--ink);
  background:
    linear-gradient(90deg, transparent 0, transparent calc(100% - 1px), var(--line) calc(100% - 1px)),
    var(--paper);
}

.chapter-hero-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 250px;
  align-items: center;
  gap: 40px;
  padding-top: 66px;
  padding-bottom: 46px;
}

.chapter-hero .kicker {
  color: var(--blue);
}

.chapter-hero h1 {
  max-width: 760px;
  margin-top: 15px;
  font-family: var(--display);
  font-size: clamp(36px, 4vw, 50px);
  font-weight: 700;
  line-height: 1.14;
  letter-spacing: -0.04em;
}

.chapter-sub {
  margin-top: 14px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 12.5px;
  letter-spacing: 0.03em;
}

.chapter-oneline {
  max-width: 620px;
  margin-top: 22px;
  color: var(--ink-soft);
  font-size: 17px;
  line-height: 1.7;
}

.chapter-figure {
  justify-self: end;
  font-family: var(--display);
  font-size: 190px;
  font-weight: 700;
  line-height: 0.8;
  color: transparent;
  -webkit-text-stroke: 1px var(--line-strong);
  user-select: none;
}

.tag-list {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 26px;
}

.tag-list li {
  padding: 4px 8px;
  border: 1px solid var(--line-strong);
  font-family: var(--mono);
  font-size: 11px;
  color: var(--muted);
  letter-spacing: 0.02em;
}

.big-idea {
  display: grid;
  grid-template-columns: 92px minmax(0, 1fr);
  gap: 22px;
  padding: 20px 0 24px;
  border-top: 1px solid var(--line);
}

.big-idea span {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.13em;
  color: var(--red);
}

.big-idea p {
  max-width: 820px;
  font-family: var(--display);
  font-size: 19px;
  font-weight: 700;
  line-height: 1.66;
  letter-spacing: -0.015em;
}

/* ---------- chapter layout ---------- */

.chapter-layout > * {
  min-width: 0;
}

.chapter-layout {
  display: grid;
  grid-template-columns: 206px minmax(0, 720px);
  justify-content: center;
  gap: 72px;
  padding-top: 60px;
  padding-bottom: 100px;
}

.toc {
  position: sticky;
  top: calc(var(--header-h) + 30px);
  align-self: start;
  min-width: 0;
  padding-top: 4px;
}

.toc > p {
  margin-bottom: 15px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--ink);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.toc ol {
  display: grid;
  gap: 2px;
  min-width: 0;
}

.toc a {
  display: grid;
  grid-template-columns: 22px minmax(0, 1fr);
  gap: 3px;
  min-width: 0;
  overflow-wrap: break-word;
  padding: 6px 0;
  color: #5c5a4e;
  font-size: 13.5px;
  line-height: 1.45;
  transition: color 0.18s;
}

.toc a span:first-child {
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--line-strong);
  padding-top: 2px;
}

.toc a:hover,
.toc a.is-active {
  color: var(--ink);
}

.toc a.is-active span:first-child {
  color: var(--blue);
}

.toc a.toc-extra {
  margin-top: 5px;
  padding-top: 9px;
  border-top: 1px dashed var(--line);
  color: var(--ink-soft);
}

.toc a.toc-extra span:first-child {
  color: var(--blue);
}

.toc .toc-cheat {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  margin-top: 22px;
  padding: 11px 12px;
  border: 1px solid var(--line-strong);
  font-size: 12.5px;
  font-weight: 600;
  white-space: nowrap;
  transition: background 0.18s, border-color 0.18s;
}

.toc-cheat:hover {
  background: var(--paper-raised);
  border-color: var(--ink);
}

/* ---------- prose ---------- */

.content-section {
  padding-bottom: 46px;
  margin-bottom: 46px;
  border-bottom: 1px solid var(--line);
}

.content-section:last-of-type {
  border-bottom: 0;
}

.section-label {
  display: flex;
  align-items: center;
  gap: 11px;
  margin-bottom: 12px;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.13em;
  color: var(--muted);
}

.section-label span:first-child {
  display: grid;
  place-items: center;
  width: 25px;
  height: 25px;
  border: 1px solid var(--line-strong);
  color: var(--blue);
  font-size: 10.5px;
  letter-spacing: 0;
}

.prose {
  min-width: 0;
}

.prose h2 {
  margin-bottom: 16px;
  font-family: var(--display);
  font-size: clamp(27px, 3vw, 34px);
  font-weight: 700;
  line-height: 1.35;
  letter-spacing: -0.03em;
}

.lead {
  margin-bottom: 22px;
  color: var(--ink-soft);
  font-size: 19px;
  line-height: 1.66;
  letter-spacing: -0.015em;
}

.prose p:not(.lead) {
  margin-bottom: 17px;
  color: var(--ink-soft);
  font-size: 16px;
  line-height: 1.78;
}

.points {
  display: grid;
  gap: 0;
  margin: 26px 0 30px;
  border-top: 1px solid var(--line);
}

.points > div {
  display: grid;
  grid-template-columns: 170px minmax(0, 1fr);
  gap: 22px;
  padding: 15px 0;
  border-bottom: 1px solid var(--line);
}

.points dt {
  font-family: var(--display);
  font-size: 15.5px;
  font-weight: 700;
  line-height: 1.55;
  letter-spacing: -0.015em;
}

.points dd {
  color: var(--ink-soft);
  font-size: 14.5px;
  line-height: 1.7;
}

.points dd code,
.prose p code,
.callout code,
.trap code {
  padding: 1px 5px;
  border: 1px solid var(--line);
  background: var(--paper-raised);
  font-family: var(--mono);
  font-size: 0.88em;
  color: var(--blue-dark);
}

/* ---------- diagram ---------- */

.diagram {
  margin: 32px 0;
  border: 1px solid var(--line-strong);
  background: var(--paper-raised);
  box-shadow: var(--shadow);
}

.diagram figcaption {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 16px;
  border-bottom: 1px solid var(--line);
  font-size: 12.5px;
  font-weight: 600;
  letter-spacing: -0.01em;
}

.diagram figcaption span {
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.1em;
  color: var(--blue);
}

.diagram-canvas {
  padding: 27px 22px;
  background-image: radial-gradient(rgba(23, 23, 15, 0.1) 0.6px, transparent 0.6px);
  background-size: 14px 14px;
}

.diagram-note {
  padding: 10px 16px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 12.5px;
  line-height: 1.6;
}

/* flow */

.flow {
  display: flex;
  align-items: stretch;
  justify-content: center;
  gap: 0;
}

.flow-step {
  position: relative;
  flex: 1 1 0;
  min-width: 0;
  padding: 13px 11px 12px;
  border: 1px solid var(--ink);
  background: var(--paper-raised);
}

.flow-step[data-tone="accent"] {
  border-color: var(--blue);
  background: var(--blue-soft);
}

.flow-step[data-tone="warn"] {
  border-color: var(--red);
  background: var(--red-soft);
}

.flow-step[data-tone="muted"] {
  border-style: dashed;
  border-color: var(--line-strong);
}

.flow-num {
  display: block;
  margin-bottom: 7px;
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--blue);
}

.flow-step b {
  display: block;
  overflow-wrap: break-word;
  font-family: var(--display);
  font-size: 14.5px;
  line-height: 1.35;
  letter-spacing: -0.02em;
}

.flow-step small {
  display: block;
  overflow-wrap: break-word;
  margin-top: 4px;
  color: var(--muted);
  font-size: 11.5px;
  line-height: 1.45;
}

.flow-arrow {
  position: relative;
  flex: 0 0 22px;
  align-self: center;
  height: 1px;
  background: var(--ink);
}

.flow-arrow::after {
  content: "";
  position: absolute;
  top: -3px;
  right: 0;
  width: 6px;
  height: 6px;
  border-top: 1px solid var(--ink);
  border-right: 1px solid var(--ink);
  transform: rotate(45deg);
}

/* compare */

.compare {
  display: grid;
  grid-template-columns: 1fr 44px 1fr;
  align-items: stretch;
}

.compare-side {
  padding: 17px 16px;
  border: 1px solid var(--line-strong);
  background: var(--paper-raised);
}

.compare-side--right {
  border-color: var(--blue);
  background: var(--blue-soft);
}

.compare-side h4 {
  padding-bottom: 9px;
  margin-bottom: 10px;
  border-bottom: 1px solid var(--line);
  font-family: var(--display);
  font-size: 15px;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.compare-side ul {
  display: grid;
  gap: 7px;
}

.compare-side li {
  position: relative;
  padding-left: 12px;
  color: var(--ink-soft);
  font-size: 13px;
  line-height: 1.55;
}

.compare-side li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 8px;
  width: 4px;
  height: 4px;
  background: var(--line-strong);
}

.compare-side--right li::before {
  background: var(--blue);
}

.compare-vs {
  display: grid;
  place-items: center;
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--muted);
}

/* stack */

.stack {
  display: grid;
  gap: 5px;
  max-width: 560px;
  margin: 0 auto;
}

.stack-layer {
  display: grid;
  grid-template-columns: 34px 1fr;
  align-items: center;
  gap: 11px;
  padding: 11px 14px;
  margin-inline: calc(var(--i) * 9px);
  border: 1px solid var(--line-strong);
  background: var(--paper-raised);
}

.stack-layer[data-tone="accent"] {
  border-color: var(--blue);
  background: var(--blue-soft);
}

.stack-layer span {
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--blue);
}

.stack-layer b {
  display: block;
  font-family: var(--display);
  font-size: 14px;
  line-height: 1.35;
}

.stack-layer small {
  display: block;
  margin-top: 2px;
  color: var(--muted);
  font-size: 11.5px;
}

/* branch */

.branch {
  max-width: 700px;
  margin: 0 auto;
}

.branch-root {
  width: min(330px, 90%);
  margin: 0 auto;
  padding: 12px 16px;
  border: 1px solid var(--ink);
  background: var(--ink);
  color: var(--paper);
  text-align: center;
}

.branch-root b {
  display: block;
  font-family: var(--display);
  font-size: 15px;
}

.branch-root small {
  display: block;
  margin-top: 3px;
  color: var(--line);
  font-size: 11.5px;
}

.branch-stem {
  width: 1px;
  height: 22px;
  margin: 0 auto;
  background: var(--ink);
}

.branch-grid {
  display: grid;
  grid-template-columns: repeat(var(--cols, 2), 1fr);
  gap: 12px;
}

.branch-card {
  padding: 13px 14px;
  border: 1px solid var(--line-strong);
  border-top: 3px solid var(--blue);
  background: var(--paper-raised);
}

.branch-card:nth-child(2n) {
  border-top-color: var(--red);
}

.branch-q {
  display: block;
  font-size: 13px;
  font-weight: 700;
  line-height: 1.45;
}

.branch-card > small {
  display: block;
  margin-top: 4px;
  color: var(--blue);
  font-family: var(--mono);
  font-size: 11px;
  line-height: 1.45;
}

.branch-card ul {
  display: grid;
  gap: 3px;
  margin-top: 8px;
  padding-top: 8px;
  border-top: 1px dashed var(--line);
}

.branch-card li {
  color: var(--muted);
  font-size: 11.5px;
  line-height: 1.5;
}

/* table */

.data-table {
  margin: 28px 0;
  border: 1px solid var(--line-strong);
  background: var(--paper-raised);
}

.data-table figcaption {
  padding: 10px 15px;
  border-bottom: 1px solid var(--line);
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.09em;
  color: var(--muted);
  text-transform: uppercase;
}

.table-scroll {
  overflow-x: auto;
}

.data-table table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
  line-height: 1.55;
}

.data-table th,
.data-table td {
  padding: 11px 14px;
  border-bottom: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

.data-table thead th {
  background: var(--paper-deep);
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.05em;
  color: var(--ink-soft);
  white-space: nowrap;
}

.data-table tbody tr:last-child td {
  border-bottom: 0;
}

.data-table tbody th {
  font-weight: 600;
  color: var(--ink);
}

.data-table td {
  color: var(--ink-soft);
}

/* callout */

.callout {
  position: relative;
  margin: 28px 0;
  padding: 15px 18px 15px 20px;
  border-left: 3px solid var(--blue);
  background: var(--blue-soft);
}

.callout--exam {
  border-color: var(--red);
  background: var(--red-soft);
}

.callout--warn {
  border-color: #a16207;
  background: #f7efdc;
}

.callout--tip {
  border-color: var(--green);
  background: var(--green-soft);
}

.callout-label {
  display: block;
  margin-bottom: 5px;
  font-family: var(--mono);
  font-size: 10.5px;
  font-weight: 600;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--blue);
}

.callout--exam .callout-label {
  color: var(--red);
}

.callout--warn .callout-label {
  color: #8a5306;
}

.callout--tip .callout-label {
  color: var(--green);
}

.callout p {
  margin: 0 !important;
  font-size: 14px !important;
  line-height: 1.65 !important;
  color: var(--ink-soft) !important;
}

.callout b {
  color: var(--ink);
}

/* exam / traps / keywords */

.exam-block {
  margin-top: 10px;
  padding: 28px 30px 30px;
  border: 1px solid var(--ink);
  background: var(--paper-raised);
  box-shadow: var(--shadow);
}

.block-heading {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 20px;
  padding-bottom: 14px;
  margin-bottom: 20px;
  border-bottom: 1px solid var(--ink);
}

.block-heading h2 {
  font-family: var(--display);
  font-size: 26px;
  font-weight: 700;
  letter-spacing: -0.03em;
}

.block-heading span {
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.13em;
  color: var(--red);
  white-space: nowrap;
}

.exam-list {
  display: grid;
  gap: 0;
  counter-reset: exam;
}

.exam-list li {
  display: grid;
  grid-template-columns: 34px 1fr;
  gap: 10px;
  padding: 13px 0;
  border-bottom: 1px dashed var(--line);
  color: var(--ink-soft);
  font-size: 14.5px;
  line-height: 1.65;
}

.exam-list li:last-child {
  border-bottom: 0;
  padding-bottom: 0;
}

.exam-list li::before {
  counter-increment: exam;
  content: counter(exam, decimal-leading-zero);
  font-family: var(--mono);
  font-size: 11px;
  color: var(--red);
  padding-top: 4px;
}

.traps {
  margin-top: 56px;
}

.trap-list {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}

.trap {
  padding: 17px 18px;
  border: 1px solid var(--line);
  background: var(--paper-raised);
}

.trap-q {
  display: block;
  margin-bottom: 7px;
  font-size: 14px;
  font-weight: 600;
  line-height: 1.5;
}

.trap-q::before {
  content: "Q.";
  margin-right: 6px;
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--red);
}

.trap-a {
  color: var(--muted);
  font-size: 13.5px;
  line-height: 1.65;
}

.trap-a::before {
  content: "→ ";
  color: var(--blue);
  font-family: var(--mono);
  font-size: 11px;
}

.keywords {
  margin-top: 44px;
  padding-top: 22px;
  border-top: 1px solid var(--line);
}

.keywords h3 {
  margin-bottom: 12px;
  font-family: var(--mono);
  font-size: 10.5px;
  font-weight: 500;
  letter-spacing: 0.13em;
  color: var(--muted);
  text-transform: uppercase;
}

.keywords ul {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.keywords li {
  padding: 4px 9px;
  border: 1px solid var(--line-strong);
  font-size: 12px;
  color: var(--ink-soft);
}

.connections {
  margin-top: 30px;
  padding: 18px 20px;
  border-left: 2px solid var(--line-strong);
  background: rgba(255, 255, 255, 0.28);
}

.connections h3 {
  margin-bottom: 7px;
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.12em;
  color: var(--muted);
}

.connections li {
  position: relative;
  padding-left: 12px;
  color: var(--muted);
  font-size: 13.5px;
  line-height: 1.65;
}

.connections li::before {
  content: "↳";
  position: absolute;
  left: 0;
  color: var(--blue);
}

/* pager */

.pager {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-top: 60px;
  padding-top: 25px;
  border-top: 1px solid var(--ink);
}

.pager a {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 15px 17px;
  border: 1px solid var(--line);
  transition: border-color 0.18s, background 0.18s;
}

.pager a:hover {
  border-color: var(--ink);
  background: var(--paper-raised);
}

.pager a.is-next {
  text-align: right;
  align-items: flex-end;
}

.pager small {
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.1em;
  color: var(--muted);
}

.pager b {
  font-family: var(--display);
  font-size: 15.5px;
  letter-spacing: -0.02em;
}

/* ---------- footer ---------- */

.site-footer {
  border-top: 1px solid var(--ink);
  background: var(--paper-deep);
}

.footer-inner {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 40px;
  padding-top: 34px;
  padding-bottom: 38px;
}

.footer-note {
  max-width: 480px;
  color: var(--muted);
  font-size: 12.5px;
  line-height: 1.7;
}

.footer-note b {
  display: block;
  margin-bottom: 5px;
  color: var(--ink);
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.12em;
  font-weight: 500;
}

.footer-links {
  display: flex;
  gap: 18px;
  font-size: 12.5px;
}

.footer-links a {
  color: var(--muted);
  border-bottom: 1px solid var(--line-strong);
  padding-bottom: 2px;
}

.footer-links a:hover {
  color: var(--ink);
  border-color: var(--ink);
}

/* ---------- search ---------- */

.search-dialog {
  position: fixed;
  inset: 0;
  z-index: 300;
  display: grid;
  place-items: start center;
  padding: 12vh 20px 20px;
  background: rgba(23, 23, 15, 0.48);
  backdrop-filter: blur(3px);
}

.search-dialog[hidden] {
  display: none;
}

.search-panel {
  width: min(620px, 100%);
  max-height: 70vh;
  overflow: hidden;
  border: 1px solid var(--ink);
  background: var(--paper);
  box-shadow: 0 30px 90px -30px rgba(0, 0, 0, 0.5);
}

.search-bar {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 13px 16px;
  border-bottom: 1px solid var(--line);
}

.search-bar span {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--blue);
}

.search-bar input {
  flex: 1;
  min-width: 0;
  border: 0;
  background: transparent;
  color: var(--ink);
  font: inherit;
  font-size: 15px;
  outline: none;
}

.search-bar input::placeholder {
  color: var(--line-strong);
}

.search-close {
  border: 1px solid var(--line);
  background: transparent;
  padding: 2px 6px;
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--muted);
  cursor: pointer;
}

.search-results {
  overflow-y: auto;
  max-height: calc(70vh - 52px);
  padding: 8px;
}

.search-empty {
  padding: 26px 16px;
  color: var(--muted);
  font-size: 14px;
  text-align: center;
}

.search-hit {
  display: block;
  padding: 10px 12px;
  border-bottom: 1px solid var(--line);
}

.search-hit:last-child {
  border-bottom: 0;
}

.search-hit:hover,
.search-hit:focus {
  background: var(--paper-raised);
}

.search-hit small {
  display: block;
  margin-bottom: 2px;
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.06em;
  color: var(--blue);
}

.search-hit b {
  display: block;
  font-size: 13.5px;
  font-weight: 600;
}

.search-hit span {
  display: block;
  margin-top: 2px;
  color: var(--muted);
  font-size: 12.5px;
  line-height: 1.5;
}

/* ---------- one page ---------- */

.onepage-body {
  background: #ddd8cc;
}

.onepage-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  width: min(210mm, calc(100% - 40px));
  margin: 0 auto;
  padding: 22px 0 14px;
}

.onepage-toolbar p {
  color: var(--ink-soft);
  font-size: 13px;
}

.onepage-toolbar p b {
  display: block;
  margin-bottom: 3px;
  font-family: var(--mono);
  font-size: 10.5px;
  letter-spacing: 0.12em;
  color: var(--muted);
}

.toolbar-actions {
  display: flex;
  gap: 8px;
  flex: none;
}

.toolbar-actions .btn {
  min-height: 38px;
  padding: 0 14px;
  font-size: 13px;
  background: var(--paper);
  border-color: var(--ink);
}

.sheet {
  width: min(210mm, calc(100% - 40px));
  min-height: 297mm;
  margin: 0 auto 40px;
  padding: 11mm 11mm 9mm;
  background: #fffdf7;
  box-shadow: 0 20px 60px -20px rgba(23, 23, 15, 0.4);
  color: #14140f;
}

.sheet-head {
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: end;
  gap: 20px;
  padding-bottom: 4mm;
  border-bottom: 1.4px solid #14140f;
}

.sheet-kicker {
  margin-bottom: 2mm;
  font-family: var(--mono);
  font-size: 8pt;
  letter-spacing: 0.14em;
  color: var(--blue);
}

.sheet-head h1 {
  font-family: var(--display);
  font-size: 21pt;
  font-weight: 700;
  line-height: 1.18;
  letter-spacing: -0.04em;
}

.sheet-head h1 span {
  color: var(--blue);
}

.sheet-sub {
  margin-top: 1.5mm;
  color: #5d5b50;
  font-size: 8.4pt;
  line-height: 1.5;
}

.sheet-stamp {
  padding: 2mm 3mm;
  border: 1px solid #14140f;
  text-align: center;
  font-family: var(--mono);
}

.sheet-stamp b {
  display: block;
  font-size: 13pt;
  line-height: 1;
}

.sheet-stamp span {
  display: block;
  margin-top: 2mm;
  font-size: 7.5pt;
  letter-spacing: 0.1em;
  color: #5d5b50;
}

.sheet-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0 5mm;
  padding-top: 3.5mm;
}

.sheet-block {
  padding: 0 0 2.6mm;
  margin-bottom: 2.8mm;
  border-bottom: 0.6px solid #d8d1c0;
  break-inside: avoid;
}

.sheet-block-head {
  display: flex;
  align-items: baseline;
  gap: 2.2mm;
  margin-bottom: 1.3mm;
}

.sheet-block-head b {
  font-family: var(--mono);
  font-size: 8pt;
  color: var(--blue);
  letter-spacing: 0.04em;
}

.sheet-block-head h2 {
  font-family: var(--display);
  font-size: 10.5pt;
  font-weight: 700;
  letter-spacing: -0.03em;
  line-height: 1.3;
}

.sheet-block ul {
  display: grid;
  gap: 0.8mm;
}

.sheet-block li {
  position: relative;
  padding-left: 3mm;
  font-size: 8.5pt;
  line-height: 1.5;
  color: #2c2b24;
}

.sheet-block li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 1.25mm;
  width: 1.1mm;
  height: 1.1mm;
  background: #9c9481;
}

.sheet-block li b {
  color: #14140f;
  font-weight: 600;
}

.sheet-block li code {
  font-family: var(--mono);
  font-size: 6.5pt;
  color: #1636a8;
}

.sheet-note {
  margin-top: 1.2mm;
  padding: 1.2mm 2mm;
  background: #f7e8e2;
  border-left: 1.5px solid #b33a24;
  font-size: 7.5pt;
  line-height: 1.45;
  color: #4a2a22;
}

.sheet-note b {
  color: #b33a24;
}

.sheet-formulas {
  grid-column: 1 / -1;
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 4mm;
  margin-top: 1mm;
  padding: 3mm 3.5mm;
  border: 1px solid #14140f;
  background: #f4f0e6;
  break-inside: avoid;
}

.formula h3 {
  margin-bottom: 1.3mm;
  font-family: var(--mono);
  font-size: 7.5pt;
  letter-spacing: 0.1em;
  color: #5d5b50;
}

.formula p {
  font-size: 8.1pt;
  line-height: 1.45;
}

.formula code {
  font-family: var(--mono);
  font-size: 7pt;
  color: #1636a8;
}

.formula small {
  display: block;
  margin-top: 1mm;
  color: #5d5b50;
  font-size: 7.5pt;
  line-height: 1.4;
}

.sheet-foot {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 10px;
  margin-top: 2mm;
  padding-top: 2mm;
  border-top: 1px solid #14140f;
  font-family: var(--mono);
  font-size: 7.5pt;
  letter-spacing: 0.05em;
  color: #6f6c60;
}

.sheet-foot b {
  color: #14140f;
}

/* ---------- reveal ---------- */

.reveal {
  opacity: 0;
  transform: translateY(14px);
  animation: rise 0.65s cubic-bezier(0.2, 0.7, 0.2, 1) forwards;
}

.reveal:nth-child(2) {
  animation-delay: 0.08s;
}

@keyframes rise {
  to {
    opacity: 1;
    transform: none;
  }
}

/* ---------- responsive ---------- */

@media (max-width: 1000px) {
  .hero {
    grid-template-columns: 1fr;
    gap: 40px;
    padding-top: 66px;
  }

  .exam-card {
    max-width: 480px;
  }

  .spine {
    grid-template-columns: repeat(4, 1fr);
    gap: 24px 0;
  }

  .spine::before {
    display: none;
  }

  .chapter-row {
    grid-template-columns: 48px minmax(0, 1fr) 30px;
  }

  .chapter-tags {
    display: none;
  }

  .chapter-layout {
    grid-template-columns: 1fr;
    gap: 34px;
  }

  .toc {
    position: static;
    padding: 18px 0;
    border-top: 1px solid var(--line);
    border-bottom: 1px solid var(--line);
  }

  .toc ol {
    grid-template-columns: repeat(3, 1fr);
    gap: 0 16px;
  }

  .toc-cheat {
    display: none;
  }

  .chapter-hero-grid {
    grid-template-columns: 1fr;
  }

  .chapter-figure {
    display: none;
  }
}

@media screen and (max-width: 900px) {
  .sheet-grid {
    grid-template-columns: 1fr 1fr;
    gap: 0 5mm;
  }

  .sheet-formulas {
    grid-template-columns: 1fr;
  }

  .sheet {
    padding: 10mm 9mm;
  }

  .sheet-block li {
    font-size: 11.5px;
    line-height: 1.55;
  }

  .sheet-block-head h2 {
    font-size: 15.5px;
  }

  .sheet-block-head b {
    font-size: 11px;
  }

  .sheet-note {
    font-size: 11.5px;
  }

  .formula h3 {
    font-size: 10.5px;
  }

  .formula p {
    font-size: 12.5px;
  }

  .formula code {
    font-size: 12px;
  }

  .formula small {
    font-size: 11px;
  }

  .sheet-foot {
    font-size: 10.5px;
  }
}

@media (max-width: 720px) {
  body {
    font-size: 16px;
  }

  .shell {
    padding: 0 20px;
  }

  .header-inner {
    gap: 10px;
  }

  .brand-text small {
    display: none;
  }

  .top-nav {
    gap: 13px;
    font-size: 13px;
  }

  .top-nav > a:first-child {
    display: none;
  }

  .search-trigger kbd {
    display: none;
  }

  .hero {
    padding-top: 48px;
    padding-bottom: 54px;
  }

  .hero h1 {
    font-size: 40px;
  }

  .hero-lede {
    font-size: 15.5px;
  }

  .hero-meta {
    font-size: 10.5px;
  }

  .spine {
    grid-template-columns: 1fr 1fr;
    gap: 22px 16px;
  }

  .spine-title {
    max-width: none;
  }

  .chapter-row {
    grid-template-columns: 32px minmax(0, 1fr) 24px;
    gap: 12px;
    padding: 18px 0;
  }

  .chapter-main strong {
    font-size: 19px;
  }

  .chapter-main small {
    font-size: 13px;
  }

  .chapter-hero-grid {
    padding-top: 44px;
    padding-bottom: 30px;
  }

  .chapter-hero h1 {
    font-size: 35px;
  }

  .chapter-figure {
    display: none;
  }

  .big-idea {
    grid-template-columns: 1fr;
    gap: 6px;
  }

  .big-idea p {
    font-size: 16px;
  }

  .chapter-layout {
    padding-top: 34px;
    padding-bottom: 64px;
  }

  .toc ol {
    grid-template-columns: 1fr 1fr;
  }

  .content-section {
    padding-bottom: 38px;
    margin-bottom: 38px;
  }

  .points > div {
    grid-template-columns: 1fr;
    gap: 4px;
  }

  .diagram-canvas {
    padding: 18px 14px;
  }

  .flow {
    flex-direction: column;
    align-items: stretch;
  }

  .flow-arrow {
    flex: 0 0 18px;
    width: 1px;
    height: 18px;
    align-self: center;
  }

  .flow-arrow::after {
    top: auto;
    right: auto;
    bottom: 0;
    left: -3px;
    transform: rotate(135deg);
  }

  .compare {
    grid-template-columns: 1fr;
    gap: 8px;
  }

  .compare-vs {
    padding: 2px 0;
  }

  .stack-layer {
    margin-inline: calc(var(--i) * 4px);
  }

  .branch-grid {
    grid-template-columns: 1fr;
  }

  .trap-list {
    grid-template-columns: 1fr;
  }

  .exam-block {
    padding: 22px 20px;
  }

  .pager {
    grid-template-columns: 1fr;
  }

  .footer-inner {
    flex-direction: column;
    gap: 20px;
  }

  .onepage-toolbar {
    flex-direction: column;
    align-items: flex-start;
  }

  .sheet {
    width: calc(100% - 24px);
    padding: 7mm;
    min-height: auto;
  }

  .sheet-grid {
    grid-template-columns: 1fr;
  }

  .sheet-formulas {
    grid-template-columns: 1fr;
  }

  .sheet {
    padding: 18px 16px 20px;
  }

  .sheet-head h1 {
    font-size: 28px;
  }

  .sheet-sub {
    font-size: 13px;
  }

  .sheet-kicker {
    font-size: 11px;
  }

  .sheet-stamp b {
    font-size: 22px;
  }

  .sheet-stamp span {
    font-size: 10.5px;
  }

  .sheet-block-head h2 {
    font-size: 17px;
  }

  .sheet-block-head b {
    font-size: 12px;
  }

  .sheet-block li {
    font-size: 14px;
    line-height: 1.6;
  }

  .sheet-note {
    font-size: 13px;
  }

  .sheet-formulas {
    gap: 16px;
    padding: 16px;
  }

  .formula h3 {
    font-size: 11px;
  }

  .formula p {
    font-size: 14px;
  }

  .formula code {
    font-size: 13px;
  }

  .formula small {
    font-size: 12.5px;
  }

  .sheet-foot {
    font-size: 10.5px;
  }
}

@media (max-width: 360px) {
  .toc ol {
    grid-template-columns: 1fr;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }

  .reveal {
    opacity: 1;
    transform: none;
  }
}

/* ---------- print ---------- */

@page {
  size: A4 portrait;
  margin: 14mm;
}

@page sheet {
  size: A4 portrait;
  margin: 0;
}

@media print {
  html,
  body {
    background: #fff;
    margin: 0;
    padding: 0;
  }

  .site-header,
  .site-footer,
  .onepage-toolbar,
  .skip {
    display: none !important;
  }

  .sheet {
    page: sheet;
    width: 210mm;
    height: 297mm;
    min-height: 297mm;
    margin: 0;
    padding: 10mm 10mm 7mm;
    box-shadow: none;
    break-inside: avoid;
    page-break-after: avoid;
  }

  .sheet-block,
  .sheet-formulas,
  .diagram,
  .data-table,
  .callout,
  .exam-block,
  .trap,
  .pager {
    break-inside: avoid;
  }

  .chapter-layout {
    display: block;
  }

  .toc {
    display: none;
  }

  .prose {
    max-width: none;
  }

  * {
    -webkit-print-color-adjust: exact;
    print-color-adjust: exact;
  }
}