/* ==========================================================================
   H446 Revision: the one stylesheet.

   1. Fonts
   2. Themes: every colour is a custom property, one block per theme
   3. Scale: type sizes, spacing, radii
   4. Base elements
   5. Layout: header, footer, page width
   6. Components: buttons, badges, progress cells, theme picker
   7. Pages: home, topic, flashcards, quiz, 404
   8. Reduced motion
   ========================================================================== */

/* 1. Fonts ---------------------------------------------------------------- */

@font-face {
  font-family: "Inter";
  font-style: normal;
  font-weight: 100 900;
  font-display: swap;
  src: url("../fonts/InterVariable.woff2") format("woff2");
}

@font-face {
  font-family: "Inter";
  font-style: italic;
  font-weight: 100 900;
  font-display: swap;
  src: url("../fonts/InterVariable-Italic.woff2") format("woff2");
}

@font-face {
  font-family: "JetBrains Mono";
  font-style: normal;
  font-weight: 400;
  font-display: swap;
  src: url("../fonts/JetBrainsMono-Regular.woff2") format("woff2");
}

@font-face {
  font-family: "JetBrains Mono";
  font-style: normal;
  font-weight: 700;
  font-display: swap;
  src: url("../fonts/JetBrainsMono-Bold.woff2") format("woff2");
}

/* 2. Themes ----------------------------------------------------------------
   Dark is the default. The inline script in base.html sets data-theme on
   <html> from localStorage before the page is drawn.
   --border is for card edges; --border-strong is for form controls, which
   need 3:1 contrast. --again marks "Again" flashcards; --danger marks a
   wrong quiz answer (always alongside a cross icon and the words "Not quite"). */

:root,
:root[data-theme="dark"] {
  color-scheme: dark;
  --bg: #0b1210;
  --surface: #121c18;
  --raised: #1a2621;
  --border: #24332c;
  --border-strong: #62796d;
  --text: #e3ece7;
  --muted: #93a79c;
  --accent: #34d399;
  --accent-text: #34d399;
  --on-accent: #04130d;
  --accent-soft: #0f2a20;
  --danger: #ff9a85;
  --danger-soft: #2c1714;
  --again: #f2b85b;
  --focus: #34d399;
}

:root[data-theme="oled"] {
  color-scheme: dark;
  --bg: #000000;
  --surface: #000000;
  --raised: #0a100d;
  --border: #1f2c26;
  --border-strong: #52695d;
  --text: #e3ece7;
  --muted: #93a79c;
  --accent: #34d399;
  --accent-text: #34d399;
  --on-accent: #04130d;
  --accent-soft: #04160e;
  --danger: #ff9a85;
  --danger-soft: #1c0907;
  --again: #f2b85b;
  --focus: #34d399;
}

:root[data-theme="light"] {
  color-scheme: light;
  --bg: #f6faf7;
  --surface: #ffffff;
  --raised: #eaf3ed;
  --border: #d5e3db;
  --border-strong: #6f8679;
  --text: #0f1f18;
  --muted: #4b5f55;
  --accent: #047857;
  --accent-text: #047857;
  --on-accent: #ffffff;
  --accent-soft: #e1f3e9;
  --danger: #b42318;
  --danger-soft: #fdebe8;
  --again: #945600;
  --focus: #047857;
}

/* 3. Scale -----------------------------------------------------------------
   Type steps follow a major third (x1.25) from a 17px body size. */

:root {
  --font-sans: "Inter", "JetBrains Mono", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, "Cascadia Mono", Menlo, Consolas, monospace;

  --step--1: 0.85rem;
  --step-0: 1.0625rem;
  --step-1: 1.33rem;
  --step-2: 1.66rem;
  --step-3: clamp(1.9rem, 1.55rem + 1.6vw, 2.6rem);
  --step-4: clamp(2.8rem, 2rem + 4vw, 4.4rem);

  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.5rem;
  --space-6: 2rem;
  --space-7: 3rem;
  --space-8: 4.5rem;

  --radius-s: 6px;
  --radius-m: 10px;
  --radius-l: 16px;

  --gutter: 1rem;
  --page: 72rem;
  --measure: 68ch;
}

@media (min-width: 48rem) {
  :root {
    --gutter: 2rem;
  }
}

/* 4. Base ------------------------------------------------------------------ */

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

html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  /* The flash a phone shows on whatever you tap: a faint mint, not blue. */
  -webkit-tap-highlight-color: color-mix(in srgb, var(--accent) 18%, transparent);
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: var(--step-0);
  line-height: 1.6;
  /* Inter: l with a tail (cv05) and I with serifs (cv08), so I, l and 1 differ. */
  font-feature-settings: "cv05" 1, "cv08" 1;
  -webkit-font-smoothing: antialiased;
  /* dvh ("dynamic viewport height") is the height actually visible, which
     changes as a phone's address bar shows and hides. vh is the fallback for
     older browsers, which ignore the dvh line. */
  min-height: 100vh;
  min-height: 100dvh;
  display: flex;
  flex-direction: column;
}

h1,
h2,
h3 {
  line-height: 1.2;
  text-wrap: balance;
  margin: 0 0 var(--space-3);
}

h1 {
  font-size: var(--step-3);
  font-weight: 700;
  letter-spacing: -0.022em;
}

h2 {
  font-size: var(--step-2);
  font-weight: 650;
  letter-spacing: -0.017em;
}

h3 {
  font-size: var(--step-1);
  font-weight: 620;
  letter-spacing: -0.01em;
}

p {
  margin: 0 0 var(--space-4);
}

a {
  color: var(--accent-text);
  text-decoration-thickness: 1px;
  text-underline-offset: 0.2em;
}

a:hover {
  text-decoration-thickness: 2px;
}

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

code,
kbd,
pre,
samp {
  font-family: var(--font-mono);
  font-feature-settings: normal;
}

code {
  font-size: 0.93em;
  padding: 0.08em 0.3em;
  border-radius: 4px;
  background: var(--raised);
  white-space: nowrap;
}

pre {
  background: var(--raised);
  border: 1px solid var(--border);
  border-radius: var(--radius-m);
  padding: var(--space-4);
  overflow-x: auto;
  line-height: 1.5;
}

pre code {
  padding: 0;
  background: none;
  white-space: pre;
}

kbd {
  font-size: 0.8em;
  padding: 0.05em 0.4em;
  border: 1px solid var(--border-strong);
  border-bottom-width: 2px;
  border-radius: 4px;
}

sup,
sub {
  line-height: 0;
}

/* Tabular figures keep scores and counts from jiggling as they change. */
.num {
  font-variant-numeric: tabular-nums;
}

.visually-hidden {
  position: absolute !important;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}

/* Parts of the page that need JavaScript are hidden without it. */
html:not(.js) .js-only {
  display: none !important;
}

.skip-link {
  position: absolute;
  left: var(--gutter);
  top: -4rem;
  padding: var(--space-2) var(--space-4);
  background: var(--accent);
  color: var(--on-accent);
  border-radius: var(--radius-s);
  font-weight: 600;
  z-index: 10;
}

.skip-link:focus {
  top: var(--space-2);
}

/* 5. Layout ---------------------------------------------------------------- */

.wrap {
  width: 100%;
  max-width: calc(var(--page) + 2 * var(--gutter));
  margin-inline: auto;
  padding-inline: var(--gutter);
}

main {
  flex: 1;
  padding-block: var(--space-5) var(--space-8);
}

/* Flashcards and quiz use one narrower column. */
main.narrow {
  max-width: calc(44rem + 2 * var(--gutter));
}

.site-header {
  border-bottom: 1px solid var(--border);
  background: var(--surface);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
  min-height: 3.75rem;
}

.brand {
  display: inline-flex;
  align-items: center;
  min-height: 2.75rem;
  gap: var(--space-2);
  color: var(--text);
  font-weight: 700;
  letter-spacing: -0.01em;
  text-decoration: none;
}

.brand-mark {
  width: 1.5rem;
  height: 1.5rem;
  fill: var(--accent);
}

.brand-mark .hollow {
  fill: none;
  stroke: var(--accent);
  stroke-width: 1.5;
}

.site-footer {
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: var(--step--1);
  padding-block: var(--space-5);
}

.site-footer p {
  margin: 0;
}

.crumbs ol {
  display: flex;
  flex-wrap: wrap;
  column-gap: var(--space-2);
  list-style: none;
  margin: calc(-1 * var(--space-3)) 0 var(--space-3);
  padding: 0;
  font-size: var(--step--1);
}

.crumbs a {
  display: inline-flex;
  align-items: center;
  min-height: 2.75rem;
}

.crumbs li {
  display: flex;
  align-items: center;
}

.crumbs li + li::before {
  content: "/";
  color: var(--muted);
  margin-right: var(--space-2);
}

/* 6. Components ------------------------------------------------------------ */

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  min-height: 2.75rem;
  padding: 0.55rem 1.1rem;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-m);
  background: var(--surface);
  color: var(--text);
  font: inherit;
  font-weight: 600;
  line-height: 1.2;
  text-decoration: none;
  cursor: pointer;
  transition: background-color 0.15s, border-color 0.15s;
}

.button:hover {
  background: var(--raised);
}

.button:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

.button svg {
  width: 1.15rem;
  height: 1.15rem;
  flex: none;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.8;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.button.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--on-accent);
}

.button.primary:hover {
  background: color-mix(in srgb, var(--accent) 85%, var(--text));
}

.button.quiet {
  background: transparent;
  border-color: var(--border);
}

.button.quiet:hover {
  background: var(--raised);
  border-color: var(--border-strong);
}

.button.small {
  min-height: 2.75rem;
  padding: 0.4rem 0.8rem;
  font-size: var(--step--1);
}

.button-note {
  font-weight: 450;
  opacity: 0.8;
  font-size: var(--step--1);
}

.badge {
  display: inline-block;
  padding: 0.05rem 0.55rem;
  border: 1px solid var(--border-strong);
  border-radius: 999px;
  color: var(--muted);
  font-size: var(--step--1);
  font-weight: 550;
  line-height: 1.5;
  white-space: nowrap;
}

/* Progress cells: one per flashcard, like the bits of a register.
   Filled = got it, bar across = again, hollow = not seen. The shapes differ
   as well as the colours, so the states are clear without colour vision. */
.cells {
  display: flex;
  flex-wrap: wrap;
  gap: 3px;
}

.cells i {
  width: 10px;
  height: 14px;
  border: 1.5px solid var(--border-strong);
  border-radius: 2px;
}

.cells i.got {
  background: var(--accent);
  border-color: var(--accent);
}

.cells i.again {
  border-color: var(--again);
  background: linear-gradient(var(--again), var(--again)) center / 100% 3px no-repeat;
}

.progress-text {
  display: flex;
  flex-wrap: wrap;
  column-gap: var(--space-4);
  margin: var(--space-2) 0 0;
  color: var(--muted);
  font-size: var(--step--1);
}

.progress-text span:empty {
  display: none;
}

.cells-key {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-1) var(--space-2);
  color: var(--muted);
  font-size: 0.8rem;
}

.cells-key .key {
  display: inline-block;
  width: 9px;
  height: 12px;
  border: 1.5px solid var(--border-strong);
  border-radius: 2px;
}

.cells-key .key:not(:first-child) {
  margin-left: var(--space-2);
}

.cells-key .key.got {
  background: var(--accent);
  border-color: var(--accent);
}

.cells-key .key.again {
  border-color: var(--again);
  background: linear-gradient(var(--again), var(--again)) center / 100% 3px no-repeat;
}

/* Theme picker: a radio group styled as a segmented control. The selected
   segment follows data-theme on <html>, so it is right before any JS runs. */
.theme-picker {
  display: flex;
  gap: 2px;
  margin: 0;
  padding: 3px;
  border: 1px solid var(--border-strong);
  border-radius: 999px;
}

.theme-picker label {
  position: relative;
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  justify-content: center;
  padding: 0.3rem 0.7rem;
  min-height: 2.75rem;
  min-width: 2.75rem;
  border-radius: 999px;
  color: var(--muted);
  font-size: var(--step--1);
  font-weight: 550;
  cursor: pointer;
}

.theme-picker label:hover {
  color: var(--text);
}

.theme-picker input {
  position: absolute;
  opacity: 0;
  width: 1px;
  height: 1px;
}

.theme-picker svg {
  width: 1.05rem;
  height: 1.05rem;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.6;
  stroke-linecap: round;
}

.theme-picker svg .solid {
  fill: currentColor;
}

.theme-picker label:has(input:focus-visible) {
  outline: 2px solid var(--focus);
  outline-offset: 1px;
}

:root[data-theme="dark"] .theme-picker label:has([value="dark"]),
:root[data-theme="oled"] .theme-picker label:has([value="oled"]),
:root[data-theme="light"] .theme-picker label:has([value="light"]) {
  background: var(--accent);
  color: var(--on-accent);
}

@media (max-width: 29.99rem) {
  /* Icons only on narrow phones; the words stay for screen readers. */
  .theme-picker label > span {
    position: absolute;
    width: 1px;
    height: 1px;
    overflow: hidden;
    clip-path: inset(50%);
    white-space: nowrap;
  }

  .theme-picker label {
    padding-inline: 0;
  }
}

/* Switch (used for Focus on the flashcards page). */
.switch {
  position: relative;
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  min-height: 2.75rem;
  font-size: var(--step--1);
  font-weight: 550;
  cursor: pointer;
}

.switch input {
  position: absolute;
  opacity: 0;
  width: 1px;
  height: 1px;
}

.switch-track {
  position: relative;
  flex: none;
  width: 2.4rem;
  height: 1.4rem;
  border: 1.5px solid var(--border-strong);
  border-radius: 999px;
  background: var(--surface);
  transition: background-color 0.15s, border-color 0.15s;
}

.switch-track::after {
  content: "";
  position: absolute;
  top: 2px;
  left: 2px;
  width: calc(1.4rem - 7px);
  height: calc(1.4rem - 7px);
  border-radius: 50%;
  background: var(--muted);
  transition: transform 0.15s;
}

.switch input:checked + .switch-track {
  background: var(--accent);
  border-color: var(--accent);
}

.switch input:checked + .switch-track::after {
  background: var(--on-accent);
  transform: translateX(1rem);
}

.switch input:focus-visible + .switch-track {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
}

/* 7. Pages ------------------------------------------------------------------ */

/* Home */

.intro {
  max-width: 44rem;
  margin-bottom: var(--space-7);
}

.intro p {
  color: var(--muted);
  font-size: var(--step-1);
  line-height: 1.45;
  margin: 0;
}

.install-note {
  max-width: 44rem;
  margin: calc(-1 * var(--space-5)) 0 var(--space-7);
  border: 1px solid var(--border);
  border-radius: var(--radius-m);
  background: var(--surface);
}

.install-note summary {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  min-height: 2.75rem;
  padding: var(--space-2) var(--space-4);
  font-weight: 600;
  cursor: pointer;
  list-style: none;
}

.install-note summary::-webkit-details-marker {
  display: none;
}

/* A chevron that turns when the note opens. */
.install-note summary::before {
  content: "";
  flex: none;
  width: 0.5rem;
  height: 0.5rem;
  border-right: 2px solid currentColor;
  border-bottom: 2px solid currentColor;
  transform: rotate(-45deg);
  transition: transform 0.15s;
}

.install-note[open] summary::before {
  transform: rotate(45deg);
}

.install-steps {
  padding: 0 var(--space-4) var(--space-2);
  font-size: var(--step--1);
}

.install-steps p {
  margin-bottom: var(--space-2);
}

.install-steps ol {
  margin: 0 0 var(--space-3);
  padding-left: 1.3rem;
}

.install-aside {
  color: var(--muted);
}

/* Not shown on computers with a mouse, or once the site is opened from the
   home screen icon (it is then running "standalone"). */
@media (hover: hover) and (pointer: fine), (display-mode: standalone) {
  .install-note {
    display: none;
  }
}

.component {
  margin-bottom: var(--space-7);
}

.component > h2 {
  display: flex;
  align-items: baseline;
  gap: var(--space-3);
  padding-bottom: var(--space-3);
  border-bottom: 2px solid var(--text);
  margin-bottom: var(--space-5);
}

.component-code {
  color: var(--accent-text);
}

.component-count {
  color: var(--muted);
  font-size: var(--step--1);
  margin: calc(-1 * var(--space-3)) 0 var(--space-4);
}

.section-title {
  font-size: var(--step-0);
  font-weight: 600;
  color: var(--muted);
  margin: var(--space-5) 0 var(--space-2);
}

.section-title .num {
  color: var(--text);
  margin-right: var(--space-1);
}

.topic-list {
  list-style: none;
  margin: 0;
  padding: 0;
  border-top: 1px solid var(--border);
}

.topic-row {
  position: relative;
  display: grid;
  grid-template-columns: 3.75rem 1fr auto;
  align-items: start;
  gap: var(--space-2) var(--space-3);
  padding: var(--space-4) var(--space-2);
  border-bottom: 1px solid var(--border);
}

.topic-row:hover {
  background: var(--surface);
}

.topic-link {
  display: contents;
  color: var(--text);
  text-decoration: none;
}

/* The whole row is clickable, via the link's stretched pseudo-element. */
.topic-link .topic-title::after {
  content: "";
  position: absolute;
  inset: 0;
}

.topic-link:focus-visible {
  outline: none;
}

.topic-row:has(.topic-link:focus-visible) {
  outline: 2px solid var(--focus);
  outline-offset: -2px;
}

.topic-row .spec {
  color: var(--accent-text);
  font-weight: 650;
}

.topic-title {
  font-weight: 600;
}

.topic-row:hover .topic-title {
  text-decoration: underline;
  text-underline-offset: 0.2em;
}

/* Spec points with no topic yet: quieter, not clickable, and labelled in
   words so the difference does not depend on colour. */
.topic-row.is-missing {
  padding-block: var(--space-3);
  color: var(--muted);
}

.topic-row.is-missing:hover {
  background: none;
}

.topic-row.is-missing .spec,
.topic-row.is-missing .topic-title {
  color: var(--muted);
  font-weight: 500;
}

.missing-note {
  margin: 0;
  font-size: var(--step--1);
}

@media (max-width: 47.99rem) {
  /* On phones the note sits beside the title, keeping each row to one line. */
  .topic-row.is-missing .missing-note {
    grid-column: 3;
    grid-row: 1;
    white-space: nowrap;
    padding-top: 0.15em;
  }
}

.topic-row .badge {
  grid-column: 3;
  grid-row: 1;
}

.topic-progress {
  grid-column: 2 / -1;
}

@media (min-width: 48rem) {
  .topic-row {
    grid-template-columns: 4.5rem minmax(0, 1fr) auto 17rem;
    align-items: center;
    padding-inline: var(--space-3);
  }

  .topic-progress {
    grid-column: 4;
    grid-row: 1;
  }
}

/* Topic */

.topic-head {
  margin-bottom: var(--space-6);
}

.spec-display {
  font-size: var(--step-4);
  font-weight: 750;
  letter-spacing: -0.035em;
  line-height: 1;
  color: var(--accent-text);
  margin: 0 0 var(--space-3);
}

.topic-head h1 {
  max-width: 24ch;
}

.topic-layout {
  display: grid;
  gap: var(--space-6);
}

.practice-actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
}

.practice .practice-actions .button {
  flex: 1 1 10rem;
  flex-direction: column;
  gap: 0;
  padding-block: var(--space-3);
}

.progress-panel {
  margin-top: var(--space-4);
  padding: var(--space-4);
  border: 1px solid var(--border);
  border-radius: var(--radius-l);
  background: var(--surface);
}

.progress-panel h3 {
  font-size: var(--step-0);
  font-weight: 650;
  margin-bottom: var(--space-3);
}

.progress-panel .cells-key {
  margin: var(--space-3) 0 var(--space-4);
}

@media (min-width: 60rem) {
  .topic-layout {
    grid-template-columns: minmax(0, var(--measure)) minmax(16rem, 20rem);
    justify-content: space-between;
    gap: var(--space-7);
  }

  .practice {
    grid-column: 2;
    grid-row: 1;
    align-self: start;
    position: sticky;
    top: var(--space-5);
  }

  .notes {
    grid-column: 1;
    grid-row: 1;
  }

  .practice .practice-actions {
    flex-direction: column;
  }

  .practice .practice-actions .button {
    flex: none;
    flex-direction: row;
    justify-content: space-between;
    gap: var(--space-2);
  }
}

/* Notes (rendered Markdown) */

.prose {
  max-width: var(--measure);
  min-width: 0;
}

.prose > :first-child {
  margin-top: 0;
}

.prose h2 {
  margin-top: var(--space-7);
}

.prose h3 {
  margin-top: var(--space-6);
}

.prose ul,
.prose ol {
  padding-left: 1.3rem;
  margin: 0 0 var(--space-4);
}

.prose li {
  margin-bottom: var(--space-2);
}

.prose li::marker {
  color: var(--muted);
}

.prose strong {
  font-weight: 650;
}

.table-wrap {
  width: fit-content;
  max-width: 100%;
  overflow-x: auto;
  margin: 0 0 var(--space-5);
  border: 1px solid var(--border);
  border-radius: var(--radius-m);
  /* Scroll shadows: a soft shade appears at an edge while there is more
     table to scroll to, so students can see a wide table scrolls. */
  background:
    linear-gradient(to right, var(--bg) 30%, transparent) left / 2.5rem 100% no-repeat local,
    linear-gradient(to left, var(--bg) 30%, transparent) right / 2.5rem 100% no-repeat local,
    radial-gradient(farthest-side at 0 50%, color-mix(in srgb, var(--text) 30%, transparent), transparent) left / 0.9rem 100% no-repeat scroll,
    radial-gradient(farthest-side at 100% 50%, color-mix(in srgb, var(--text) 30%, transparent), transparent) right / 0.9rem 100% no-repeat scroll;
}

.prose table,
.prompt table {
  border-collapse: collapse;
  font-size: 0.95em;
  font-variant-numeric: tabular-nums;
}

.prose th,
.prose td,
.prompt th,
.prompt td {
  padding: 0.55rem 0.8rem;
  text-align: left;
  vertical-align: top;
  border-bottom: 1px solid var(--border);
}

.prose tr:last-child td,
.prompt tr:last-child td {
  border-bottom: 0;
}

.prose th,
.prompt th {
  background: var(--raised);
  font-weight: 650;
  white-space: nowrap;
}

.notes-end {
  margin-top: var(--space-7);
  padding-top: var(--space-5);
  border-top: 1px solid var(--border);
}

.notes-end p {
  font-weight: 600;
  margin-bottom: var(--space-3);
}

/* Flashcards and quiz headers */

.page-head {
  margin-bottom: var(--space-5);
}

.page-head h1 {
  margin-bottom: var(--space-1);
}

.page-sub {
  color: var(--muted);
  margin: 0;
}

.page-sub .num {
  color: var(--accent-text);
  font-weight: 650;
  margin-right: var(--space-1);
}

/* Flashcards */

.fc-toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-2) var(--space-4);
  margin-bottom: var(--space-3);
}

.fc-position {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin: 0;
  font-weight: 600;
}

.fc-chip {
  font-size: var(--step--1);
  font-weight: 600;
  padding: 0 0.5rem;
  border-radius: 999px;
  border: 1.5px solid currentColor;
}

.fc-chip.got {
  color: var(--accent-text);
}

.fc-chip.again {
  color: var(--again);
}

.fc-tools {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.fc-cells {
  margin-bottom: var(--space-4);
}

.fc-cells .cells i.current {
  outline: 2px solid var(--text);
  outline-offset: 1px;
}

.fc-deck {
  list-style: none;
  margin: 0;
  padding: 0;
}

.fc-face {
  padding: var(--space-5);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-l);
  background: var(--raised);
}

.fc-label {
  color: var(--muted);
  font-size: var(--step--1);
  font-weight: 600;
  margin-bottom: var(--space-2);
}

.fc-text > :last-child {
  margin-bottom: 0;
}

.fc-front .fc-text {
  font-size: var(--step-1);
  font-weight: 600;
  line-height: 1.35;
  letter-spacing: -0.01em;
}

.fc-back .fc-text {
  font-size: var(--step-0);
}

/* Without JavaScript every card is listed, question then answer. */
html:not(.js) .fc-card {
  display: grid;
  gap: var(--space-2);
  margin-bottom: var(--space-5);
}

html:not(.js) .fc-inner {
  display: grid;
  gap: var(--space-2);
}

/* With JavaScript one card shows at a time and flips over. */
.js .fc-card {
  display: none;
  /* Let the browser handle vertical scrolling, and give horizontal swipes
     to flashcards.js. */
  touch-action: pan-y;
  perspective: 1400px;
  cursor: pointer;
}

.js .fc-card.is-current {
  display: block;
}

.js .fc-inner {
  display: grid;
  transform-style: preserve-3d;
  transition: transform 0.5s cubic-bezier(0.2, 0.7, 0.2, 1);
}

.js .fc-face {
  grid-area: 1 / 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
  min-height: 15rem;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}

.js .fc-front {
  /* Safari only hides the back of a flipped face if the face has a
     transform of its own, even one that does nothing. */
  transform: rotateY(0deg);
}

.js .fc-back {
  transform: rotateY(180deg);
  border-color: var(--accent);
}

.js .fc-card.is-flipped .fc-inner {
  transform: rotateY(180deg);
}

/* Belt and braces for browsers that ignore backface-visibility: the hidden
   face is also made invisible, switching exactly halfway through the 0.5s
   turn, when the card is edge-on. With reduced motion the switch is instant. */
.js .fc-face {
  transition: visibility 0s linear 0.25s;
}

.js .fc-back,
.js .fc-card.is-flipped .fc-front {
  visibility: hidden;
}

.js .fc-card.is-flipped .fc-back {
  visibility: visible;
}

.fc-done {
  touch-action: pan-y;
  padding: var(--space-6) var(--space-5);
  border: 1px dashed var(--border-strong);
  border-radius: var(--radius-l);
  text-align: center;
}

.fc-done .practice-actions {
  justify-content: center;
}

.fc-done:focus {
  outline: none;
}

.fc-controls {
  margin-top: var(--space-4);
  display: grid;
  gap: var(--space-3);
}

.fc-nav {
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: var(--space-3);
}

.fc-mark {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-3);
}

.fc-mark .button {
  min-height: 3.25rem;
}

.button.mark-again {
  border-color: var(--again);
  color: var(--again);
  border-width: 1.5px;
}

.button.mark-got {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--on-accent);
}

.button.mark-got:hover {
  background: color-mix(in srgb, var(--accent) 85%, var(--text));
}

.fc-hint {
  color: var(--muted);
  font-size: var(--step--1);
  text-align: center;
  margin: var(--space-2) 0 0;
}

@media (max-width: 29.99rem) {
  .fc-nav .nav-label {
    position: absolute;
    width: 1px;
    height: 1px;
    overflow: hidden;
    clip-path: inset(50%);
  }

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

/* Keyboard hint on computers, swipe hint on touch screens. */
.fc-hint-touch {
  display: none;
}

@media (hover: none) and (pointer: coarse) {
  .fc-hint {
    display: none;
  }

  .fc-hint.fc-hint-touch {
    display: block;
  }

  /* A long press to swipe should not start selecting text. */
  .js .fc-card {
    -webkit-user-select: none;
    user-select: none;
    -webkit-touch-callout: none;
  }
}

/* On phones the flashcards page fills exactly the visible height (100dvh via
   body): the card stretches to fill the space, so the Got it / Again buttons
   sit just above the bottom of the screen instead of under the address bar.
   On a short screen the card keeps its minimum height and the page scrolls. */
@media (max-width: 47.99rem) {
  .fc-page {
    display: flex;
    flex-direction: column;
    padding-bottom: var(--space-4);
  }

  .fc-page .page-head {
    margin-bottom: var(--space-3);
  }

  /* Give the card the room: the breadcrumb already names the topic, and the
     footer note is on every other page. */
  .js .fc-page .page-sub {
    display: none;
  }

  .js body:has(.fc-page) .site-footer {
    display: none;
  }

  .js .fc-page .flashcards {
    flex: 1;
    display: flex;
    flex-direction: column;
  }

  .js .fc-page .fc-deck {
    flex: 1;
    display: flex;
    flex-direction: column;
  }

  .js .fc-page .fc-card.is-current {
    flex: 1;
    display: flex;
    flex-direction: column;
  }

  .js .fc-page .fc-inner {
    flex: 1;
  }

  .js .fc-page .fc-face {
    min-height: 12rem;
  }

  .js .fc-page .fc-cells {
    margin-bottom: var(--space-3);
  }

  .js .fc-page .fc-controls {
    margin-top: var(--space-3);
  }
}

@media (min-width: 48rem) {
  .js .fc-face {
    min-height: 19rem;
    padding: var(--space-6);
  }

  .fc-front .fc-text {
    font-size: var(--step-2);
  }

  .fc-back .fc-text {
    font-size: var(--step-1);
    line-height: 1.5;
  }
}

/* Quiz */

.quiz-status {
  display: flex;
  justify-content: space-between;
  color: var(--muted);
  font-size: var(--step--1);
  font-weight: 600;
}

.quiz-status p {
  margin: 0 0 var(--space-2);
}

.meter {
  height: 4px;
  border-radius: 2px;
  background: var(--border);
  margin-bottom: var(--space-5);
  overflow: hidden;
}

.meter span {
  display: block;
  height: 100%;
  background: var(--accent);
}

/* The list of questions: what shows without JavaScript. quiz.js hides it
   and shows one question at a time instead. */
.js .quiz-list {
  display: none;
}

.quiz-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: var(--space-5);
}

.quiz-q {
  padding: var(--space-4) var(--space-5);
  border: 1px solid var(--border);
  border-radius: var(--radius-m);
  background: var(--surface);
}

.quiz-options {
  margin: var(--space-3) 0;
  padding-left: 1.6rem;
}

.quiz-options li {
  margin-bottom: var(--space-2);
}

.quiz-answer summary {
  display: flex;
  align-items: center;
  min-height: 2.75rem;
  font-weight: 600;
  cursor: pointer;
}

.quiz-answer > :last-child {
  margin-bottom: 0;
}

.quiz fieldset {
  border: 0;
  margin: 0;
  padding: 0;
  min-width: 0;
}

.difficulty {
  margin: 0 0 var(--space-2);
  line-height: 1;
}

.pips {
  display: inline-flex;
  gap: 4px;
}

.pips i {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  border: 1.5px solid var(--muted);
}

.pips i.on {
  background: var(--muted);
}

.prompt {
  font-size: var(--step-1);
  font-weight: 600;
  line-height: 1.4;
  letter-spacing: -0.01em;
}

.prompt:focus {
  outline: none;
}

.prompt > :last-child {
  margin-bottom: 0;
}

/* A table in a question (e.g. a Karnaugh map) uses body text, not the
   larger bold prompt text. */
.prompt .table-wrap {
  margin: var(--space-4) 0 0;
  font-size: var(--step-0);
  font-weight: 400;
  letter-spacing: 0;
}

.options {
  display: grid;
  gap: 0.875rem;
  margin: var(--space-5) 0;
}

.option {
  display: flex;
  align-items: flex-start;
  min-height: 3.25rem;
  gap: var(--space-3);
  padding: 0.85rem var(--space-4);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-m);
  background: var(--surface);
  cursor: pointer;
  transition: background-color 0.15s, border-color 0.15s;
}

.option:hover {
  background: var(--raised);
}

.option:has(input:checked) {
  border-color: var(--accent);
  background: var(--accent-soft);
  box-shadow: inset 0 0 0 1px var(--accent);
}

.option:has(input:focus-visible) {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
}

.option input {
  appearance: none;
  flex: none;
  width: 1.25rem;
  height: 1.25rem;
  margin: 0.15rem 0 0;
  border: 2px solid var(--border-strong);
  border-radius: 50%;
  background: var(--surface);
}

.option input:checked {
  border-color: var(--accent);
  background: radial-gradient(var(--accent) 0 40%, transparent 45%);
}

.option input:focus-visible {
  outline: none;
}

.option-text {
  min-width: 0;
}

/* Long expressions in an answer may wrap between symbols on a phone,
   rather than running under the "Your answer" label. */
.option-text code {
  white-space: normal;
  -webkit-box-decoration-break: clone;
  box-decoration-break: clone;
}

.verdict {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  padding: var(--space-3) var(--space-4);
  margin-bottom: var(--space-5);
  border: 1.5px solid;
  border-radius: var(--radius-m);
  font-size: var(--step-1);
  font-weight: 700;
}

.verdict:focus {
  outline: none;
}

.verdict p {
  margin: 0;
}

.verdict svg {
  width: 1.9rem;
  height: 1.9rem;
  flex: none;
  fill: none;
  stroke: currentColor;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.verdict.is-right {
  color: var(--accent-text);
  background: var(--accent-soft);
  border-color: var(--accent);
}

.verdict.is-wrong {
  color: var(--danger);
  background: var(--danger-soft);
  border-color: var(--danger);
}

.results {
  list-style: none;
  padding: 0;
  margin: var(--space-4) 0 var(--space-5);
  display: grid;
  gap: var(--space-2);
}

.result {
  display: flex;
  flex-wrap: wrap;
  align-items: flex-start;
  gap: var(--space-1) var(--space-3);
  padding: 0.75rem var(--space-4);
  border: 1px solid var(--border);
  border-radius: var(--radius-m);
  color: var(--muted);
}

.result-icon {
  flex: none;
  width: 1.25rem;
  height: 1.25rem;
  margin-top: 0.15rem;
}

.result-icon svg {
  width: 100%;
  height: 100%;
  fill: none;
  stroke: currentColor;
  stroke-width: 2.2;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.result .option-text {
  flex: 1 1 12rem;
}

.result-note {
  margin-left: auto;
  font-size: var(--step--1);
  font-weight: 650;
}

.result.is-answer {
  color: var(--text);
  border-color: var(--accent);
  background: var(--accent-soft);
}

.result.is-answer .result-icon,
.result.is-answer .result-note {
  color: var(--accent-text);
}

.result.is-chosen:not(.is-answer) {
  color: var(--text);
  border-color: var(--danger);
  background: var(--danger-soft);
}

.result.is-chosen:not(.is-answer) .result-icon,
.result.is-chosen:not(.is-answer) .result-note {
  color: var(--danger);
}

.explanation {
  margin: 0 0 var(--space-5);
  padding: var(--space-4) var(--space-5);
  border-left: 3px solid var(--accent);
  background: var(--surface);
  border-radius: 0 var(--radius-m) var(--radius-m) 0;
}

.explanation h2 {
  font-size: var(--step-0);
  font-weight: 700;
  margin-bottom: var(--space-1);
}

.explanation > :last-child {
  margin-bottom: 0;
}

.summary h2 {
  font-size: var(--step-1);
  color: var(--muted);
}

.summary h2:focus {
  outline: none;
}

.big-score {
  font-size: var(--step-4);
  font-weight: 750;
  letter-spacing: -0.03em;
  line-height: 1;
  color: var(--accent-text);
  margin-bottom: var(--space-4);
}

.big-score span {
  color: var(--muted);
  font-size: 0.5em;
  font-weight: 600;
  letter-spacing: 0;
}

.best {
  font-weight: 650;
}

.summary .practice-actions {
  margin-top: var(--space-5);
}

/* Exam questions */

.intro .intro-actions {
  margin-top: var(--space-5);
  font-size: var(--step-0);
}

.intro-actions .button {
  flex-direction: column;
  align-items: flex-start;
  gap: 0;
  padding-block: var(--space-3);
}

.exam-source {
  max-width: 44rem;
  margin: calc(-1 * var(--space-5)) 0 var(--space-6);
  padding: var(--space-3) var(--space-4);
  border-left: 3px solid var(--border-strong);
  color: var(--muted);
  font-size: var(--step--1);
}

.exam-source p {
  margin: 0;
}

.exam-side .exam-source {
  margin: 0 0 var(--space-4);
}

.exam-notes-links {
  margin: var(--space-2) 0 0;
}

.exam-notes-links a {
  display: inline-flex;
  align-items: center;
  min-height: 2.75rem;
  font-weight: 600;
}

.exam-layout {
  display: grid;
  /* minmax(0, ...) lets the column shrink to the screen, so the scrolling
     strip of question numbers cannot widen the page. */
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-5);
}

.exam-side {
  min-width: 0;
}

.exam-side h2 {
  font-size: var(--step-0);
  font-weight: 650;
  margin-bottom: var(--space-3);
}

.exam-side .progress-panel {
  margin: 0 0 var(--space-4);
}

.exam-score {
  margin: 0 0 var(--space-3);
}

.exam-jump ol {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
}

.exam-jump a {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 2.75rem;
  min-height: 2.75rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-s);
  color: var(--text);
  font-weight: 600;
  text-decoration: none;
}

.exam-jump a:hover {
  background: var(--raised);
  border-color: var(--border-strong);
}

/* A question you have marked: filled, with a tick, so it does not rely on colour. */
.exam-jump a.is-marked {
  background: var(--accent-soft);
  border-color: var(--accent);
}

.exam-jump a.is-marked::after {
  content: "✓";
  margin-left: 0.15em;
  font-size: 0.8em;
  color: var(--accent-text);
}

/* On phones the list of question numbers sits in a scrolling strip. */
@media (max-width: 59.99rem) {
  .exam-jump ol {
    flex-wrap: nowrap;
    overflow-x: auto;
    padding-bottom: var(--space-2);
  }

  .exam-jump li {
    flex: none;
  }
}

.exam-questions {
  display: grid;
  gap: var(--space-6);
  min-width: 0;
}

.exam-q {
  min-width: 0;
  padding: var(--space-4);
  border: 1px solid var(--border);
  border-radius: var(--radius-l);
  background: var(--surface);
  scroll-margin-top: var(--space-4);
}

.exam-q-head {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: var(--space-2) var(--space-4);
  padding-bottom: var(--space-3);
  margin-bottom: var(--space-4);
  border-bottom: 1px solid var(--border);
}

.exam-q-head h2 {
  font-size: var(--step-1);
  margin: 0;
}

.exam-q-head p {
  margin: 0;
  color: var(--muted);
  font-weight: 600;
}

.exam-diagram-note {
  display: flex;
  align-items: flex-start;
  gap: var(--space-2);
  margin: 0 0 var(--space-4);
  padding: var(--space-3);
  border: 1px dashed var(--border-strong);
  border-radius: var(--radius-m);
  color: var(--muted);
  font-size: var(--step--1);
}

.exam-diagram-note svg {
  width: 1.25rem;
  height: 1.25rem;
  flex: none;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.5;
  stroke-linejoin: round;
}

.exam-part + .exam-part {
  margin-top: var(--space-5);
  padding-top: var(--space-4);
  border-top: 1px dashed var(--border);
}

.exam-part-head {
  display: flex;
  justify-content: space-between;
  gap: var(--space-3);
  margin: 0 0 var(--space-2);
  font-weight: 700;
}

.exam-label {
  color: var(--accent-text);
}

.exam-marks {
  color: var(--muted);
}

.exam-text,
.mark-scheme .prose {
  max-width: none;
  overflow-wrap: anywhere;
}

/* Long bits of code in a sentence may wrap on a phone (code blocks still scroll). */
.exam-text :not(pre) > code,
.mark-scheme :not(pre) > code {
  white-space: normal;
}

.exam-text > :last-child,
.ms-answer > :last-child,
.ms-guidance .prose > :last-child {
  margin-bottom: 0;
}

.exam-text pre,
.mark-scheme pre {
  font-size: 0.85em;
}

/* A Mermaid diagram drawn by diagrams.js, with its code in a
   "Diagram as text" section underneath. Wide diagrams scroll sideways. */
.diagram {
  margin: 0 0 var(--space-4);
}

.diagram-drawing {
  overflow-x: auto;
}

.diagram.is-drawn .diagram-drawing {
  padding: var(--space-3);
  border: 1px solid var(--border);
  border-radius: var(--radius-m);
  background: var(--surface);
}

.diagram-drawing svg {
  display: block;
  max-width: 100%;
  height: auto;
  margin: 0 auto;
}

.diagram-text summary {
  display: inline-flex;
  align-items: center;
  min-height: 44px;
  color: var(--accent-text);
  cursor: pointer;
}

.diagram-text pre {
  margin-top: 0;
}

.mark-scheme {
  margin-top: var(--space-4);
  border: 1px solid var(--border);
  border-radius: var(--radius-m);
  background: var(--bg);
}

.mark-scheme summary {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  min-height: 2.75rem;
  padding: var(--space-2) var(--space-4);
  font-weight: 600;
  cursor: pointer;
}

.mark-scheme summary::-webkit-details-marker {
  display: none;
}

/* The same chevron as "Add to your home screen": right when closed, down when open. */
.mark-scheme summary::before {
  content: "";
  flex: none;
  width: 0.5rem;
  height: 0.5rem;
  margin-right: var(--space-1);
  border-right: 2px solid currentColor;
  border-bottom: 2px solid currentColor;
  transform: rotate(-45deg);
  transition: transform 0.15s;
}

.mark-scheme[open] summary::before {
  transform: rotate(45deg);
}

.mark-scheme summary span {
  color: var(--muted);
}

.mark-scheme[open] summary {
  border-bottom: 1px solid var(--border);
}

.ms-row {
  padding: var(--space-4);
}

.ms-row + .ms-row {
  border-top: 1px solid var(--border);
}

.ms-label {
  margin: 0 0 var(--space-2);
  font-weight: 700;
  color: var(--accent-text);
}

.ms-label span {
  color: var(--muted);
  font-weight: 500;
}

.ms-guidance {
  margin-top: var(--space-4);
  padding: var(--space-3) var(--space-4);
  border-radius: var(--radius-s);
  background: var(--raised);
  font-size: var(--step--1);
}

.ms-guidance-head {
  margin: 0 0 var(--space-2);
  font-weight: 700;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  font-size: 0.75rem;
}

/* Answering and marking a part ------------------------------------------- */

.written-answer,
.auto-mark {
  margin-top: var(--space-4);
}

.written-answer label,
.answer-box label,
.part-mark label {
  display: block;
  margin-bottom: var(--space-2);
  font-weight: 600;
}

.written-answer textarea,
.answer-line input {
  width: 100%;
  min-height: 2.75rem;
  padding: 0.55rem 0.75rem;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-s);
  background: var(--bg);
  color: var(--text);
  font: inherit;
}

.written-answer textarea {
  resize: vertical;
  line-height: 1.5;
}

.answer-box + .answer-box {
  margin-top: var(--space-4);
}

.answer-line {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  max-width: 32rem;
}

/* Expressions and values use the mono font, so ∧ ∨ ¬ ⊻ show and digits line up. */
.answer-line input {
  font-family: var(--font-mono);
  font-feature-settings: normal;
}

.answer-box.is-right input {
  border-color: var(--accent);
}

.answer-box.is-wrong input {
  border-color: var(--danger);
}

.box-result svg {
  display: block;
  width: 1.6rem;
  height: 1.6rem;
  fill: none;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.answer-box.is-right .box-result svg {
  stroke: var(--accent-text);
}

.answer-box.is-wrong .box-result svg {
  stroke: var(--danger);
}

.symbol-keys {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-top: var(--space-2);
}

.symbol-keys .button {
  min-width: 2.75rem;
  font-family: var(--font-mono);
  font-size: var(--step-0);
}

.auto-actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-top: var(--space-4);
}

.auto-verdict:not(:empty) {
  margin-top: var(--space-4);
}

.auto-verdict p {
  margin: var(--space-2) 0 0;
}

.auto-verdict .verdict {
  display: inline-flex;
  margin-bottom: 0;
  font-size: var(--step-0);
}

.auto-verdict .verdict svg {
  width: 1.5rem;
  height: 1.5rem;
}

.auto-problem {
  color: var(--danger);
  font-weight: 600;
}

.auto-hint {
  color: var(--muted);
}

/* Mark points: tick the ones your answer makes. */
.ms-how {
  margin: 0;
  padding: var(--space-3) var(--space-4) 0;
  color: var(--muted);
  font-size: var(--step--1);
}

.ms-points {
  margin: 0 0 var(--space-3);
  padding-left: 1.4em;
}

.js .ms-points.has-ticks {
  list-style: none;
  padding-left: 0;
}

.js .has-ticks .ms-point {
  display: flex;
  align-items: flex-start;
  gap: var(--space-3);
  min-height: 2.75rem;
  padding: var(--space-2);
  margin: 0 calc(-1 * var(--space-2));
  border-radius: var(--radius-s);
  cursor: pointer;
}

.js .has-ticks .ms-point:hover {
  background: var(--raised);
}

.ms-point input {
  flex: none;
  width: 1.4rem;
  height: 1.4rem;
  margin: 0.1rem 0 0;
  accent-color: var(--accent);
  cursor: pointer;
}

.ms-point .prose > :last-child {
  margin-bottom: 0;
}

.ms-point:has(input:checked) .prose {
  color: var(--text);
  font-weight: 550;
}

.part-mark {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-2) var(--space-4);
  margin-top: var(--space-4);
}

.part-mark label {
  margin: 0;
}

.part-mark[hidden] {
  display: none;
}

.part-mark input {
  width: 4.5rem;
  min-height: 2.75rem;
  padding: 0.4rem 0.6rem;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-s);
  background: var(--bg);
  color: var(--text);
  font: inherit;
  font-weight: 650;
  font-variant-numeric: tabular-nums;
  text-align: center;
}

.question-total {
  margin: var(--space-5) 0 0;
  padding-top: var(--space-4);
  border-top: 1px solid var(--border);
  font-weight: 650;
}

.question-total:empty {
  display: none;
}

.self-mark {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-2) var(--space-4);
  margin-top: var(--space-5);
  padding-top: var(--space-4);
  border-top: 1px solid var(--border);
}

.self-mark label {
  font-weight: 600;
}

.self-mark-input {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  color: var(--muted);
}

.self-mark input {
  width: 4.5rem;
  min-height: 2.75rem;
  padding: 0.4rem 0.6rem;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-s);
  background: var(--bg);
  color: var(--text);
  font: inherit;
  font-weight: 650;
  font-variant-numeric: tabular-nums;
  text-align: center;
}

@media (min-width: 48rem) {
  .exam-q {
    padding: var(--space-5) var(--space-6);
  }
}

@media (min-width: 60rem) {
  .exam-layout {
    grid-template-columns: minmax(14rem, 17rem) minmax(0, 1fr);
    gap: var(--space-7);
    align-items: start;
  }

  .exam-side {
    position: sticky;
    top: var(--space-5);
    max-height: calc(100vh - 2 * var(--space-5));
    max-height: calc(100dvh - 2 * var(--space-5));
    overflow-y: auto;
  }
}

/* 404 */

.not-found {
  max-width: 36rem;
  padding-top: var(--space-6);
}

.not-found-code {
  margin: 0 0 var(--space-3);
  line-height: 1;
}

.not-found-code code {
  font-size: clamp(3.5rem, 2.5rem + 6vw, 6.5rem);
  font-weight: 700;
  color: var(--accent-text);
  background: none;
  padding: 0;
  letter-spacing: -0.04em;
}

.not-found .aside {
  color: var(--muted);
  font-size: var(--step--1);
}

/* 8. Reduced motion -------------------------------------------------------
   The flashcard swaps sides instantly and nothing else moves. */

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    transition-duration: 0s !important;
    transition-delay: 0s !important;
    animation-duration: 0s !important;
    scroll-behavior: auto !important;
  }
}