@font-face {
  font-family: "Atkinson Hyperlegible Mono";
  src: url("assets/atkinson-mono-400.woff2") format("woff2");
  font-weight: 400;
  font-style: normal;
  font-display: swap;
}

@font-face {
  font-family: "Atkinson Hyperlegible Mono";
  src: url("assets/atkinson-mono-700.woff2") format("woff2");
  font-weight: 700;
  font-style: normal;
  font-display: swap;
}

html {
  font-size: 12px;
}

@media only screen and (min-width: 1400px) { html { font-size: 13px } }
@media only screen and (min-width: 1600px) { html { font-size: 14px } }
@media only screen and (min-width: 1800px) { html { font-size: 16px } }
@media only screen and (min-width: 2048px) { html { font-size: 18px } }
@media only screen and (max-height: 600px) { html { font-size: 10px } }

:root {
  color-scheme: light;
  --accent: #e85000;
  --accent-bright: #ff6a1a;
  --ink: #111111;
  --gray: #888888;
  --line: #cccccc;
  --soft: #eeeeee;
  --font: "Atkinson Hyperlegible Mono", "Overpass Mono", monospace;
}

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

body {
  margin: 0;
  padding: 0;
  background: white;
  color: #222222;
  font-family: var(--font);
  font-size: 1.33rem;
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

a {
  text-decoration: none;
  color: var(--accent);
}

::selection {
  background: var(--accent);
  color: white;
}

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

h1,
h2,
h3,
p {
  margin-top: 0;
}

a:focus-visible,
button:focus-visible,
input:focus-visible,
textarea:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 3px;
}

.skip-link {
  position: fixed;
  z-index: 1000;
  top: 1rem;
  left: 1rem;
  padding: 0.8rem 1.2rem;
  background: var(--ink);
  color: white;
  font-size: 1.1rem;
  transform: translateY(-250%);
}

.skip-link:focus {
  transform: translateY(0);
}

/* Layout (custom elements, sci-hub style) */

fixed-width {
  margin: 0 auto;
  padding: 2.33rem;
  max-width: 1700px;
  overflow-x: hidden;
  display: block;
}

column-split {
  display: flex;
  align-items: flex-start;
  width: 100%;
}

row-split,
.vertical {
  display: flex;
  flex-direction: column;
  align-items: center;
}

column-left {
  flex-grow: 1;
}

block-space {
  margin-top: 3rem;
  display: block;
}

block-rounded {
  border: dotted 2px var(--line);
  border-radius: 2rem;
  padding: 2.88rem;
  display: block;
}

header-small {
  display: block;
  font-size: 1.66rem;
  font-weight: 700;
  margin: 1rem 0;
  color: var(--accent);
}

.section-head {
  margin: 0 0 2rem;
  text-align: center;
  font-size: inherit;
  font-weight: 400;
}

.section-head header-small {
  margin: 0 0 0.5rem;
}

.section-head p {
  margin: 0;
  color: var(--gray);
  font-size: 1.22rem;
}

/* Hero (.open) */

.open {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  width: 100%;
  gap: 3rem;
  padding: 0;
}

.hero-brand {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  width: 100%;
  margin: 0 0 3rem;
}

.hero-fox {
  position: relative;
  z-index: 1;
  display: block;
  width: 57.143%;
  max-width: 250px;
  height: auto;
  margin: 0 0 -15px;
}

.hero-wordmark {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 100%;
  height: 120px;
  margin: 0;
  background: var(--accent);
  color: white;
  font-family: Baskerville, "Baskerville Old Face", "Times New Roman", serif;
  font-size: 9rem;
  font-weight: 400;
  line-height: 1;
  text-align: center;
}

.open .side {
  width: min(269px, 61.143%);
  text-align: center;
}

.open .note {
  margin: 0 0 2rem;
  padding: 1.2rem;
  border: solid 2px #aaaaaa;
  border-radius: 1.33rem;
  background: white;
  font-size: 1.22rem;
  line-height: 1.8;
}

.open .note b {
  color: var(--accent);
}

.open .go {
  display: inline-grid;
  place-items: center;
  width: 12rem;
  aspect-ratio: 1;
  border: solid 4px white;
  border-radius: 50%;
  background: var(--accent);
  color: white;
  font-size: 1.9rem;
  font-weight: 700;
  line-height: 1.4;
}

.open .go:hover {
  border-width: 8px;
}

/* Nav squares (.languages) */

.languages {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  margin: 2rem 0;
}

.language {
  display: grid;
  place-items: center;
  height: 3.4rem;
  aspect-ratio: 1;
  margin: 0.4rem;
  border: dashed 1px #777777;
  border-radius: 0.4rem;
  background: white;
  color: #555555;
  font-size: 1rem;
  line-height: 1.2;
  text-align: center;
}

.language:hover {
  background: var(--accent);
  border-color: var(--accent);
  color: white;
  font-weight: 700;
}

.language.selected {
  border: solid 1px black;
  color: #333333;
  font-weight: 700;
}

.language.selected:hover {
  background: white;
  border-color: black;
  color: #555555;
}

/* Counter */

.counter {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  width: fit-content;
  margin: 0 auto;
  padding: 2rem 0.8rem;
  background: var(--soft);
  border-radius: 1.77rem;
}

.counter > div {
  margin: 1rem;
  width: 13rem;
  padding: 1.22rem;
  background: white;
  border: solid 1px #888888;
  border-radius: 12px;
  font-size: 1.12rem;
}

.counter span {
  display: block;
}

.counter .number {
  margin-top: 0.88rem;
  color: var(--accent);
  font-size: 1.44rem;
  font-weight: 700;
}

/* Motto */

.motto {
  max-width: 62rem;
  margin: 0 auto;
  padding: 0 2rem;
  color: var(--gray);
  font-size: 2.3rem;
  font-weight: 700;
  line-height: 1.6;
  text-align: center;
}

.motto em {
  color: var(--accent);
  font-style: normal;
}

/* Promo (.bot style) */

.promo {
  max-width: 90rem;
  margin: 0 auto;
}

.promo .header {
  margin: 0;
  color: #333333;
  font-size: 2.6rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.promo .header .accent {
  color: var(--accent);
}

.promo .text {
  margin-top: 1.2rem;
  max-width: 64rem;
  font-size: 1.22rem;
}

.promo .text b {
  display: inline-block;
  padding: 0.2rem 0.5rem;
  border-radius: 0.88rem;
  background: #888888;
  color: white;
  font-weight: 400;
}

.promo .text b.hot {
  background: var(--accent);
}

.promo .question {
  margin-top: 1rem;
  font-size: 1.33rem;
}

.promo .question .arrow {
  display: none;
  font-size: 2rem;
  font-weight: 700;
  color: var(--accent);
}

.promo .question:hover .arrow {
  display: inline-block;
}

.exam-heading {
  margin: 2rem 0 0;
  color: var(--ink);
  font-size: 1.33rem;
}

.exam-links {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.8rem;
  max-width: 76rem;
  margin-top: 1rem;
}

.exam-link {
  display: flex;
  align-items: center;
  gap: 1rem;
  min-height: 4.6rem;
  padding: 0.9rem 1.2rem;
  border: solid 1px var(--line);
  border-radius: 0.8rem;
  background: white;
  color: var(--ink);
  font-size: 1.12rem;
  line-height: 1.4;
}

.exam-link:hover {
  border-color: var(--accent);
  background: var(--soft);
}

.exam-code {
  flex: 0 0 5rem;
  color: var(--accent);
  font-size: 1rem;
  font-weight: 700;
}

.promo-kicker {
  margin: 0 0 0.4rem;
  color: var(--accent);
  font-size: 1rem;
  font-weight: 700;
  letter-spacing: 0.12em;
}

.promo-it {
  padding: 2.5rem;
  border: dotted 2px var(--accent);
  border-radius: 2rem;
  background: #fff9f5;
}

/* IT fundamentals */

.learning-page {
  background: #fbfaf7;
}

.learning-page fixed-width {
  max-width: 1200px;
}

.learning-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 2rem;
  padding-bottom: 1.5rem;
  border-bottom: dotted 2px var(--line);
}

.learning-header .languages {
  margin: 0;
}

.learning-brand {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  color: var(--ink);
}

.learning-brand img {
  flex: 0 0 auto;
}

.learning-brand-name {
  font-family: Baskerville, "Baskerville Old Face", "Times New Roman", serif;
  font-size: 2.4rem;
  line-height: 1;
}

.learning-brand-course {
  padding: 0.25rem 0.6rem;
  border-radius: 999px;
  background: var(--accent);
  color: white;
  font-size: 0.9rem;
  font-weight: 700;
}

.course-main,
.lesson-main {
  max-width: 980px;
  margin: 0 auto;
}

.breadcrumbs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
  margin: 1.5rem 0 2rem;
  color: var(--gray);
  font-size: 1rem;
}

.breadcrumbs a {
  color: #555555;
  text-decoration: underline;
  text-underline-offset: 0.2em;
}

.eyebrow {
  margin: 0 0 0.8rem;
  color: var(--accent);
  font-size: 1rem;
  font-weight: 700;
  letter-spacing: 0.12em;
}

.course-hero {
  padding: clamp(2.5rem, 6vw, 5rem);
  border: solid 2px var(--ink);
  border-radius: 2rem;
  background:
    linear-gradient(135deg, rgba(232, 80, 0, 0.08), transparent 48%),
    white;
}

.course-hero h1 {
  max-width: 780px;
  margin: 0;
  color: var(--ink);
  font-size: clamp(2.8rem, 7vw, 5.6rem);
  line-height: 1.2;
  letter-spacing: -0.05em;
}

.course-hero h1 em {
  color: var(--accent);
  font-style: normal;
}

.course-lead {
  max-width: 700px;
  margin: 2rem 0 0;
  color: #444444;
  font-size: 1.3rem;
}

.primary-link {
  display: inline-flex;
  align-items: center;
  gap: 1rem;
  margin-top: 2.3rem;
  padding: 1rem 1.4rem;
  border: solid 2px var(--accent);
  border-radius: 0.8rem;
  background: var(--accent);
  color: white;
  font-weight: 700;
}

.primary-link:hover {
  background: white;
  color: var(--accent);
}

.learning-principles {
  margin-top: 5rem;
}

.principle-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
}

.principle-grid article {
  padding: 1.7rem;
  border: solid 1px var(--line);
  border-radius: 1.2rem;
  background: white;
}

.principle-number {
  display: block;
  color: var(--accent);
  font-size: 1rem;
  font-weight: 700;
}

.principle-grid h3 {
  margin: 0.8rem 0 0.5rem;
  color: var(--ink);
  font-size: 1.3rem;
}

.principle-grid p {
  margin: 0;
  color: #555555;
  font-size: 1.08rem;
}

.course-path {
  margin-top: 5rem;
  padding: clamp(2rem, 5vw, 3.5rem);
  border-radius: 2rem;
  background: var(--ink);
  color: white;
}

.path-heading {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 2rem;
  margin-bottom: 2rem;
}

.path-heading h2 {
  margin: 0;
  font-size: 2rem;
}

.path-heading > p {
  max-width: 31rem;
  margin: 0;
  color: #cccccc;
  font-size: 1.05rem;
}

.lesson-card {
  position: relative;
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 0.5rem 1rem;
  padding: 1.6rem;
  border: solid 1px #555555;
  border-radius: 1.1rem;
}

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

.lesson-catalog .lesson-card {
  height: 100%;
}

.lesson-catalog .lesson-card + .lesson-card {
  margin-top: 0;
}

.lesson-card + .lesson-card {
  margin-top: 1rem;
}

.lesson-card-active {
  background: white;
  color: var(--ink);
}

.lesson-card-active:hover {
  border-color: var(--accent);
  box-shadow: inset 0 0 0 1px var(--accent);
}

.lesson-order {
  color: var(--accent);
  font-size: 0.95rem;
  font-weight: 700;
}

.lesson-status {
  align-self: start;
  padding: 0.2rem 0.6rem;
  border-radius: 999px;
  background: var(--soft);
  color: #555555;
  font-size: 0.85rem;
}

.lesson-card strong {
  grid-column: 1 / -1;
  font-size: 1.65rem;
}

.lesson-description {
  color: #555555;
  font-size: 1.08rem;
}

.lesson-go {
  color: var(--accent);
  font-weight: 700;
}

.lesson-card-soon {
  color: #dddddd;
}

.lesson-card-soon .lesson-description {
  color: #aaaaaa;
}

.lesson-card-soon .lesson-status {
  background: #333333;
  color: #bbbbbb;
}

.mascot-note {
  display: grid;
  grid-template-columns: auto 1fr;
  align-items: center;
  gap: 2rem;
  margin-top: 4rem;
  padding: 2rem;
  border: dotted 2px var(--line);
  border-radius: 2rem;
  background: white;
}

.mascot-placeholder {
  display: grid;
  place-items: center;
  width: 7rem;
  aspect-ratio: 1;
  border: dashed 2px var(--accent);
  border-radius: 50%;
  color: var(--accent);
  font-size: 3rem;
  font-weight: 700;
}

.mascot-note h2 {
  margin: 0 0 0.5rem;
  color: var(--ink);
  font-size: 1.55rem;
}

.mascot-note p:last-child {
  margin: 0;
  color: #555555;
  font-size: 1.1rem;
}

.lesson-hero {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  align-items: center;
  gap: 3rem;
  padding: clamp(2rem, 6vw, 4rem);
  border: solid 2px var(--ink);
  border-radius: 2rem;
  background: white;
}

.lesson-hero h1 {
  margin: 0;
  color: var(--ink);
  font-size: clamp(3rem, 7vw, 5.5rem);
  line-height: 1.1;
  letter-spacing: -0.05em;
}

.lesson-lead {
  max-width: 610px;
  margin: 1.5rem 0 0;
  color: #444444;
  font-size: 1.3rem;
}

.lesson-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  margin: 2rem 0 0;
}

.lesson-meta div {
  min-width: 9rem;
  padding-right: 1rem;
  border-right: dotted 1px var(--line);
}

.lesson-meta dt {
  color: var(--accent);
  font-size: 0.85rem;
  font-weight: 700;
}

.lesson-meta dd {
  margin: 0.2rem 0 0;
  color: #555555;
  font-size: 0.95rem;
}

.binary-hero-mark {
  display: grid;
  grid-template-columns: 1fr 1fr;
  overflow: hidden;
  width: clamp(11rem, 22vw, 17rem);
  aspect-ratio: 1;
  border: solid 2px var(--ink);
  border-radius: 50%;
  background: var(--ink);
}

.binary-hero-mark span {
  display: grid;
  place-items: center;
  color: white;
  font-size: clamp(3rem, 7vw, 6rem);
  font-weight: 700;
}

.binary-hero-mark span:last-child {
  background: var(--accent);
}

.script-notice {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 1.2rem;
  margin: 2rem 0 4rem;
  padding: 1.3rem 1.5rem;
  border-left: solid 4px var(--accent);
  background: #fff2ea;
}

.script-notice-icon {
  color: var(--accent);
}

.script-notice strong {
  color: var(--ink);
}

.script-notice p {
  margin: 0.2rem 0 0;
  color: #555555;
  font-size: 1rem;
}

.scene-list {
  display: grid;
  gap: 2rem;
}

.lesson-scene {
  padding: clamp(1.6rem, 5vw, 3rem);
  border: solid 1px var(--line);
  border-radius: 2rem;
  background: white;
}

.scene-heading {
  display: flex;
  align-items: center;
  gap: 1.3rem;
  margin-bottom: 2rem;
}

.scene-number {
  display: grid;
  flex: 0 0 auto;
  place-items: center;
  width: 4.4rem;
  aspect-ratio: 1;
  border-radius: 50%;
  background: var(--accent);
  color: white;
  font-size: 1.15rem;
  font-weight: 700;
}

.scene-heading p {
  margin: 0;
  color: var(--accent);
  font-size: 0.95rem;
  font-weight: 700;
}

.scene-heading h2 {
  margin: 0.2rem 0 0;
  color: var(--ink);
  font-size: clamp(1.5rem, 4vw, 2.1rem);
  line-height: 1.3;
}

.scene-screen {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.7rem;
  padding: 2rem;
  border-radius: 1.2rem;
  background: var(--ink);
  color: white;
  text-align: center;
}

.scene-screen span {
  padding: 0.7rem;
  border: solid 1px #777777;
  border-radius: 0.6rem;
}

.scene-screen b,
.scene-screen strong {
  grid-column: 1 / -1;
}

.scene-screen b {
  color: var(--accent-bright);
  font-size: 2rem;
}

.scene-screen strong {
  color: white;
  font-size: 1.7rem;
}

.voice-card {
  margin-top: 1.5rem;
  padding: 1.4rem 1.5rem;
  border-left: solid 4px var(--accent);
  border-radius: 0 1rem 1rem 0;
  background: #fff7f2;
}

.voice-meta {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 0.6rem;
  color: var(--accent);
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.08em;
}

.voice-id {
  color: var(--gray);
}

.voice-card p {
  margin: 0;
  color: #333333;
  font-size: 1.18rem;
}

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

.state-pair > div,
.use-pair > div {
  display: grid;
  place-items: center;
  gap: 0.6rem;
  min-height: 11rem;
  padding: 1.5rem;
  border: solid 1px var(--line);
  border-radius: 1.2rem;
  text-align: center;
}

.state-light {
  width: 3rem;
  aspect-ratio: 1;
  border-radius: 50%;
  background: #555555;
  box-shadow: 0 0 0 0.5rem #eeeeee;
}

.state-light.is-on {
  background: var(--accent-bright);
  box-shadow: 0 0 1.5rem 0.5rem rgba(255, 106, 26, 0.3);
}

.state-pair small {
  color: #555555;
}

.state-pair strong,
.use-pair strong {
  color: var(--accent);
  font-size: 3rem;
  line-height: 1;
}

.number-system-compare {
  display: grid;
  gap: 1rem;
}

.number-system-compare div {
  padding: 1.4rem;
  border: solid 1px var(--line);
  border-radius: 1rem;
}

.number-system-compare small {
  display: block;
  color: #666666;
}

.number-system-compare strong {
  display: block;
  margin-top: 0.5rem;
  color: var(--ink);
  font-size: clamp(1.2rem, 4vw, 2rem);
  letter-spacing: 0.08em;
}

.counting-line {
  display: grid;
  gap: 0.5rem;
  margin-top: 1rem;
  padding: 1.3rem;
  border-radius: 1rem;
  background: var(--ink);
  color: white;
  overflow-x: auto;
  white-space: nowrap;
}

.counting-line small {
  display: inline-block;
  width: 7rem;
  color: var(--accent-bright);
  font-weight: 700;
}

.place-value-row {
  display: grid;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: 0.7rem;
}

.place-value-row span {
  display: grid;
  place-items: center;
  aspect-ratio: 1;
  border: solid 2px var(--ink);
  border-radius: 1rem;
  color: var(--ink);
  font-size: clamp(1.4rem, 5vw, 2.4rem);
  font-weight: 700;
}

.place-value-row span:last-child {
  border-color: var(--accent);
  background: var(--accent);
  color: white;
}

.screen-caption {
  margin: 1rem 0 0;
  color: var(--accent);
  font-weight: 700;
  text-align: center;
}

.use-pair strong {
  font-size: 4rem;
}

.use-pair span {
  color: #444444;
}

.big-equation {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: clamp(0.6rem, 3vw, 1.5rem);
  min-height: 11rem;
  padding: 1.5rem;
  border-radius: 1.2rem;
  background: var(--ink);
  color: white;
  font-size: clamp(1.5rem, 5vw, 2.8rem);
}

.big-equation strong {
  color: var(--accent-bright);
}

.big-equation b {
  padding: 0.3rem 0.7rem;
  border-radius: 0.5rem;
  background: #333333;
}

.big-equation.compact {
  min-height: auto;
  margin-top: 1rem;
}

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

.binary-table {
  width: 100%;
  min-width: 520px;
  border-collapse: collapse;
  text-align: center;
}

.binary-table th,
.binary-table td {
  padding: 1rem 0.8rem;
  border: solid 1px var(--line);
}

.binary-table th:first-child {
  width: 9rem;
  color: #555555;
  font-size: 0.95rem;
  text-align: left;
}

.binary-table thead th {
  background: var(--soft);
}

.binary-answer-row td {
  background: #fff2ea;
  color: var(--accent);
  font-size: 1.8rem;
  font-weight: 700;
}

.binary-conclusion {
  margin: 1.2rem 0 0;
  color: #555555;
  font-size: clamp(1.6rem, 5vw, 2.5rem);
  text-align: center;
}

.binary-conclusion strong {
  color: var(--accent);
}

.binary-conclusion sub {
  font-size: 0.45em;
}

.quiz-options {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.8rem;
  margin: 1.5rem 0 0;
  padding: 0;
  list-style: none;
}

.quiz-options li {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 1rem;
  padding: 1.2rem;
  border: solid 2px var(--line);
  border-radius: 1rem;
}

.quiz-options span {
  display: grid;
  place-items: center;
  width: 2rem;
  aspect-ratio: 1;
  border-radius: 50%;
  background: var(--soft);
  color: #555555;
  font-weight: 700;
}

.quiz-options code {
  color: var(--ink);
  font-family: var(--font);
  font-size: 1.6rem;
  font-weight: 700;
}

.quiz-answer {
  margin-top: 1rem;
  border: solid 2px var(--accent);
  border-radius: 1rem;
  background: white;
}

.quiz-answer summary {
  padding: 1.1rem 1.3rem;
  color: var(--accent);
  cursor: pointer;
  font-weight: 700;
}

.quiz-answer summary:hover {
  background: #fff7f2;
}

.answer-reveal {
  padding: 0 1.3rem 1.3rem;
}

.answer-title {
  margin: 0;
  padding: 1rem;
  border-radius: 0.8rem;
  background: var(--accent);
  color: white;
  text-align: center;
}

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

.branch-grid .voice-card {
  height: calc(100% - 1.5rem);
}

.voice-card.is-correct {
  border-left-color: #218739;
  background: #f1faf3;
}

.voice-card.is-correct .voice-speaker {
  color: #218739;
}

.voice-card.is-retry {
  border-left-color: #cf9b00;
  background: #fff9e8;
}

.voice-card.is-retry .voice-speaker {
  color: #846300;
}

.summary-rule {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(14rem, 1fr));
  gap: 1rem;
}

.summary-rule p {
  display: grid;
  place-items: center;
  min-height: 8rem;
  margin: 0;
  padding: 1rem;
  border: solid 2px var(--ink);
  border-radius: 1rem;
  color: var(--ink);
  text-align: center;
}

.summary-rule strong {
  color: var(--accent);
  font-size: 1.35rem;
}

.lesson-finish {
  margin: 2rem 0 0;
  color: var(--ink);
  font-size: clamp(1.5rem, 4vw, 2.2rem);
  font-weight: 700;
  text-align: center;
}

.lesson-end-nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 2rem;
}

.lesson-end-nav a {
  padding: 0.9rem 1.2rem;
  border: solid 1px var(--line);
  border-radius: 0.8rem;
  background: white;
  color: #444444;
}

.lesson-end-nav a:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.quantity-visual {
  display: grid;
  gap: 1.5rem;
  padding: 2rem;
  border-radius: 1.2rem;
  background: var(--ink);
  color: white;
  text-align: center;
}

.quantity-dots {
  display: flex;
  justify-content: center;
  gap: 0.7rem;
}

.quantity-dots span {
  width: 2.2rem;
  aspect-ratio: 1;
  border-radius: 50%;
  background: var(--accent-bright);
}

.quantity-equivalence {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 0.8rem;
  margin: 0;
  font-size: clamp(1.6rem, 5vw, 2.6rem);
}

.quantity-equivalence strong {
  color: var(--accent-bright);
}

.quantity-equivalence sub {
  font-size: 0.45em;
}

.radix-example-grid,
.use-case-grid,
.logic-gate-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 1rem;
}

.radix-example-grid > div,
.use-case-grid > div,
.logic-gate-card {
  padding: 1.4rem;
  border: solid 1px var(--line);
  border-radius: 1rem;
  background: white;
}

.radix-example-grid small,
.use-case-grid small,
.logic-gate-card small {
  display: block;
  color: var(--accent);
  font-size: 0.85rem;
  font-weight: 700;
}

.radix-example-grid strong,
.use-case-grid strong,
.logic-gate-card strong {
  display: block;
  margin-top: 0.5rem;
  color: var(--ink);
  font-size: 1.25rem;
}

.radix-example-grid p,
.use-case-grid p,
.logic-gate-card p {
  margin: 0.6rem 0 0;
  color: #555555;
  font-size: 1rem;
}

.symbol-strip {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.55rem;
  padding: 1.5rem;
  border-radius: 1.2rem;
  background: var(--ink);
}

.symbol-strip span {
  display: grid;
  place-items: center;
  width: 3.2rem;
  aspect-ratio: 1;
  border: solid 1px #666666;
  border-radius: 0.7rem;
  color: white;
  font-size: 1.45rem;
  font-weight: 700;
}

.symbol-strip span.is-letter,
.symbol-strip span.is-focus {
  border-color: var(--accent-bright);
  background: var(--accent);
}

.symbol-strip.value-strip span {
  width: auto;
  min-width: 5rem;
  aspect-ratio: auto;
  padding: 0.8rem;
}

.formula-panel {
  display: grid;
  gap: 0.7rem;
  padding: clamp(1.5rem, 4vw, 2.2rem);
  border-radius: 1.2rem;
  background: var(--ink);
  color: white;
  text-align: center;
}

.formula-panel p {
  margin: 0;
}

.formula-panel .formula-main {
  color: white;
  font-size: clamp(1.5rem, 5vw, 2.5rem);
  font-weight: 700;
}

.formula-panel .formula-main strong,
.formula-panel .formula-result {
  color: var(--accent-bright);
}

.formula-panel .formula-note {
  color: #bbbbbb;
  font-size: 1rem;
}

.formula-panel sub {
  font-size: 0.45em;
}

.bit-group-demo {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 1rem;
  padding: 1.5rem;
  border: solid 1px var(--line);
  border-radius: 1.2rem;
  text-align: center;
}

.bit-group-demo > div {
  display: grid;
  gap: 0.5rem;
}

.bit-group-demo small {
  color: #666666;
}

.bit-group-demo code {
  color: var(--ink);
  font-family: var(--font);
  font-size: clamp(1.4rem, 5vw, 2.3rem);
  font-weight: 700;
}

.bit-group-demo b {
  color: var(--accent);
  font-size: 2rem;
}

.calculation-rules {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.8rem;
}

.calculation-rule {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1.1rem 1.3rem;
  border: solid 1px var(--line);
  border-radius: 0.9rem;
}

.calculation-rule code {
  color: var(--ink);
  font-family: var(--font);
  font-size: 1.35rem;
  font-weight: 700;
}

.calculation-rule span {
  color: #666666;
  font-size: 0.95rem;
}

.calculation-board {
  padding: 1.8rem;
  border-radius: 1.2rem;
  background: var(--ink);
  color: white;
  overflow-x: auto;
}

.calculation-board pre {
  width: fit-content;
  margin: 0 auto;
  color: white;
  font-family: var(--font);
  font-size: clamp(1.5rem, 5vw, 2.3rem);
  font-weight: 700;
  line-height: 1.45;
}

.calculation-board .carry {
  color: var(--accent-bright);
}

.overflow-panel {
  display: grid;
  gap: 1rem;
  padding: 1.7rem;
  border: solid 2px var(--accent);
  border-radius: 1.2rem;
  background: #fff7f2;
}

.overflow-panel p {
  margin: 0;
  color: #444444;
}

.overflow-panel strong {
  color: var(--accent);
  font-size: 1.4rem;
}

.logic-gate-card {
  text-align: center;
}

.logic-gate-card code {
  display: inline-block;
  margin-top: 0.7rem;
  padding: 0.35rem 0.65rem;
  border-radius: 0.5rem;
  background: var(--ink);
  color: white;
  font-family: var(--font);
  font-size: 1rem;
}

.condition-example {
  margin: 1rem 0 0;
  padding: 1.2rem;
  border-left: solid 4px var(--accent);
  background: var(--soft);
  color: #333333;
  font-weight: 700;
}

.truth-table-compact {
  min-width: 400px;
}

.truth-table-compact td:last-child {
  color: var(--accent);
  font-size: 1.25rem;
  font-weight: 700;
}

.bitwise-board {
  display: grid;
  gap: 0.55rem;
  padding: 1.6rem;
  border-radius: 1.2rem;
  background: var(--ink);
  color: white;
}

.bitwise-row {
  display: grid;
  grid-template-columns: 5.5rem 1fr;
  gap: 1rem;
  padding: 0.35rem 0;
  border-bottom: solid 1px #444444;
}

.bitwise-row:last-child {
  border-bottom: 0;
}

.bitwise-row span {
  color: var(--accent-bright);
  font-weight: 700;
}

.bitwise-row code {
  color: white;
  font-family: var(--font);
  font-size: 1.35rem;
  letter-spacing: 0.15em;
}

span.rotate {
  display: inline-block;
  color: var(--accent);
  font-size: 1.88rem;
  animation: spin 3s linear infinite;
}

@keyframes spin {
  from { transform: rotate(0deg) }
  to { transform: rotate(360deg) }
}

/* Article cards (.recent) */

.recent {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

.article {
  display: block;
  width: 44%;
  max-width: 64rem;
  height: fit-content;
  margin: 2rem 2% 0;
  padding: 1.6rem;
  border: solid 2px var(--soft);
  border-radius: 1rem;
  background: white;
  color: var(--ink);
  overflow-x: hidden;
}

.article:hover {
  border: dashed 2px #888888;
}

.article .meta {
  display: flex;
  justify-content: space-between;
  color: var(--gray);
  font-size: 1.1rem;
  font-weight: 700;
}

.article .title {
  margin: 1rem 0;
  color: var(--ink);
  font-size: 1.66rem;
  font-weight: 700;
}

.article .journal,
.article .year {
  color: #555555;
  font-size: 1.22rem;
}

.article .abstract {
  margin-top: 1rem;
  color: #333333;
  font-size: 1.22rem;
}

/* Steps (block-date) */

block-date {
  display: block;
  flex: 0 0 auto;
  min-width: 6rem;
  padding: 1rem;
  border-radius: 1rem;
  color: white;
  font-size: 1.66rem;
  font-weight: 700;
  text-align: center;
}

block-date.black {
  background: black;
}

block-date.accent {
  background: var(--accent);
}

block-date.white {
  border: dotted 2px var(--accent);
  background: white;
  color: var(--accent);
}

block-date.gray {
  border: none;
  border-radius: 0;
  border-bottom: dotted 2px #333333;
  background: white;
  color: #333333;
  font-weight: 400;
}

.step {
  display: flex;
  align-items: center;
  gap: 2rem;
  max-width: 72rem;
  margin: 2rem auto 0;
}

.step .body {
  flex: 1;
}

.step h3 {
  margin: 0 0 0.4rem;
  color: var(--ink);
  font-size: 1.44rem;
}

.step p {
  margin: 0;
  color: #555555;
  font-size: 1.22rem;
}

.step-arrow {
  margin: 0.6rem 0;
  color: var(--gray);
  font-size: 2rem;
  font-weight: 700;
  text-align: center;
}

/* Vision */

block-rounded.vision {
  border-color: var(--ink);
  background: var(--ink);
  color: white;
}

block-rounded.vision header-small {
  color: var(--accent-bright);
}

block-rounded.vision .big {
  margin-bottom: 1.5rem;
  font-size: 2.3rem;
  font-weight: 700;
  line-height: 1.5;
  letter-spacing: -0.02em;
}

block-rounded.vision .text {
  color: #dddddd;
  font-size: 1.22rem;
}

block-rounded.vision b.pill {
  display: inline-block;
  margin: 0.3rem;
  padding: 0.3rem 0.8rem;
  border-radius: 0.88rem;
  background: var(--accent);
  color: white;
  font-weight: 400;
}

/* Info block (about) */

block-rounded.info h2 {
  margin: 0 0 2rem;
  color: #333333;
  font-size: 1.66rem;
  font-weight: 700;
}

block-rounded.info .lead {
  font-size: 1.22rem;
}

.facts {
  margin: 2rem 0 0;
}

.facts > div {
  display: grid;
  grid-template-columns: 14rem 1fr;
  gap: 1.5rem;
  padding: 1.2rem 0;
  border-bottom: dotted 2px var(--line);
  font-size: 1.22rem;
}

.facts > div:first-child {
  border-top: dotted 2px var(--line);
}

.facts dt {
  color: var(--accent);
  font-weight: 700;
}

.facts dd {
  margin: 0;
  color: #333333;
}

/* Contact */

.contact {
  padding: 3rem;
  border-radius: 1.77rem;
  background: var(--soft);
  text-align: center;
}

.contact .big {
  margin-bottom: 1rem;
  color: var(--ink);
  font-size: 2.3rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.contact p {
  color: #555555;
  font-size: 1.22rem;
}

.contact .mail {
  display: inline-block;
  margin-top: 1.5rem;
  padding: 0.4rem 1rem;
  border-radius: 0.88rem;
  font-size: 1.66rem;
  font-weight: 700;
}

.contact .mail:hover {
  background: var(--accent);
  color: white;
}

.contact-form {
  max-width: 62rem;
  margin: 2rem auto 0;
  text-align: left;
}

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

.contact-form label {
  display: block;
  margin-bottom: 1rem;
  color: var(--ink);
  font-size: 1.12rem;
  font-weight: 700;
}

.contact-form label > span {
  display: block;
  margin-bottom: 0.4rem;
}

.contact-form input,
.contact-form textarea {
  width: 100%;
  border: solid 1px #888888;
  border-radius: 0.8rem;
  background: white;
  color: var(--ink);
  font: inherit;
  font-size: 1.22rem;
}

.contact-form input {
  min-height: 3.8rem;
  padding: 0.7rem 0.9rem;
}

.contact-form textarea {
  min-height: 12rem;
  padding: 0.9rem;
  resize: vertical;
}

.contact-form .form-trap {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

.turnstile-wrap {
  display: flex;
  justify-content: center;
  margin: 1.5rem 0;
}

.contact-form button {
  display: block;
  min-height: 4.2rem;
  margin: 0 auto;
  padding: 0.8rem 1.5rem;
  border: solid 3px white;
  border-radius: 1rem;
  background: var(--accent);
  color: white;
  cursor: pointer;
  font: inherit;
  font-size: 1.33rem;
  font-weight: 700;
}

.contact-form button:hover {
  border-color: var(--ink);
}

.contact .form-status {
  min-height: 1.8em;
  margin: 1rem 0 0;
  color: var(--ink);
  font-weight: 700;
  text-align: center;
}

.contact .form-status[data-state="success"] {
  color: #176b2b;
}

.contact .form-status[data-state="error"] {
  color: #a12c00;
}

.contact .form-policy {
  margin: 0.8rem 0 0;
  font-size: 1rem;
  text-align: center;
}

/* Legal pages */

block-rounded.legal {
  max-width: 76rem;
  margin: 0 auto;
}

block-rounded.legal h1 {
  margin: 0 0 2rem;
  color: var(--ink);
  font-size: 2.3rem;
  line-height: 1.4;
}

block-rounded.legal h2 {
  margin: 2.5rem 0 0.8rem;
  color: var(--ink);
  font-size: 1.44rem;
}

block-rounded.legal p {
  font-size: 1.22rem;
}

.draft-note {
  padding: 1rem 1.2rem;
  border-left: solid 4px var(--accent);
  background: var(--soft);
}

.privacy-contact {
  color: var(--accent);
  font-weight: 700;
}

/* Footer (.mirrors) */

.mirrors {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  margin: 3rem 0 1rem;
}

.mirror {
  display: grid;
  place-items: center;
  height: 5rem;
  aspect-ratio: 1;
  margin: 0.6rem;
  border: solid 1px #777777;
  border-radius: 50%;
  background: white;
  color: #555555;
  font-size: 1.05rem;
  line-height: 1.2;
  text-align: center;
}

.mirror:hover {
  border-color: var(--accent);
  background: var(--accent);
  color: white;
  font-weight: 700;
}

.mirror.selected {
  border-color: var(--accent);
  background: var(--accent);
  color: white;
  font-weight: 700;
}

.copyright {
  margin: 1rem 0 2rem;
  color: var(--gray);
  font-size: 1.1rem;
  text-align: center;
}

/* 404 */

.error-wrap {
  max-width: 62rem;
  margin: 4rem auto;
  text-align: center;
}

.error-code {
  margin: 0 0 1rem;
  color: var(--accent);
  font-size: 6rem;
  font-weight: 700;
  line-height: 1;
}

.error-wrap h1 {
  color: var(--ink);
  font-size: 2rem;
}

.error-wrap p {
  color: #555555;
}

/* Responsive */

@media only screen and (max-width: 1024px) {
  fixed-width {
    padding: 1.88rem;
  }

  .article {
    width: auto;
    max-width: 80vw;
    margin: 2rem 0 0;
  }
}

@media only screen and (max-width: 640px) {
  .hero-wordmark {
    font-size: 7rem;
  }

  .open .go {
    width: 10rem;
    font-size: 1.5rem;
  }

  .motto {
    font-size: 1.8rem;
  }

  .promo .header {
    font-size: 2rem;
  }

  .exam-links {
    grid-template-columns: 1fr;
  }

  .promo-it {
    padding: 1.8rem;
  }

  .learning-header {
    align-items: flex-start;
    flex-direction: column;
  }

  .learning-brand-name {
    font-size: 2rem;
  }

  .principle-grid,
  .lesson-catalog,
  .radix-example-grid,
  .use-case-grid,
  .logic-gate-grid,
  .calculation-rules,
  .state-pair,
  .use-pair,
  .quiz-options,
  .branch-grid,
  .summary-rule {
    grid-template-columns: 1fr;
  }

  .path-heading {
    align-items: flex-start;
    flex-direction: column;
  }

  .lesson-card {
    grid-template-columns: 1fr;
  }

  .lesson-card strong {
    grid-column: auto;
  }

  .lesson-status {
    justify-self: start;
  }

  .mascot-note {
    grid-template-columns: 1fr;
  }

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

  .binary-hero-mark {
    width: 10rem;
  }

  .lesson-meta {
    flex-direction: column;
  }

  .lesson-meta div {
    border-right: 0;
  }

  .scene-heading {
    align-items: flex-start;
  }

  .scene-number {
    width: 3.6rem;
  }

  .lesson-end-nav {
    flex-direction: column;
  }

  .bit-group-demo {
    grid-template-columns: 1fr;
  }

  .bit-group-demo b {
    transform: rotate(90deg);
  }

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

  block-rounded {
    padding: 1.8rem;
  }

  block-rounded.vision .big,
  .contact .big {
    font-size: 1.8rem;
  }

  .step {
    align-items: flex-start;
    gap: 1.2rem;
  }

  .facts > div {
    grid-template-columns: 1fr;
    gap: 0.3rem;
  }

  .counter > div {
    width: 100%;
    margin: 0.6rem 1rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  span.rotate {
    animation: none;
  }
}