/* =============================================================
   FIELD NOTES — Study app views (Study / Glossary / Practice / Progress)
   Layered on top of tokens.css; legacy app.css still drives the visualizer.
   ============================================================= */

.app-shell { min-height: 100vh; background: var(--bg); color: var(--ink); }

/* ─── Masthead ─────────────────────────────────────────────── */
.fn-masthead {
  display: grid;
  grid-template-columns: 1fr auto;
  grid-template-rows: auto auto;
  gap: var(--s-3) var(--s-7);
  padding: var(--s-6) var(--s-7) 0;
  border-bottom: 1.5px solid var(--ink);
  background: var(--bg);
}
.fn-mast-title { grid-column: 1 / 2; grid-row: 1; }
.fn-mast-title .eyebrow { display: block; margin-bottom: var(--s-1); }
.fn-mast-title h1 {
  margin: 0;
  font-size: var(--t-3xl);
  font-weight: 400;
  letter-spacing: -0.015em;
  line-height: 1.05;
}
.fn-mast-title .fn-tagline {
  margin: var(--s-1) 0 0;
  font-style: italic;
  color: var(--ink-3);
  font-size: var(--t-lg);
  max-width: 64ch;
  text-wrap: pretty;
}
.fn-mast-controls {
  grid-column: 2 / 3; grid-row: 1;
  display: flex; align-items: flex-start; gap: var(--s-3);
}

.fn-tabs {
  grid-column: 1 / -1; grid-row: 2;
  display: flex; gap: 0;
  margin: var(--s-5) calc(var(--s-7) * -1) 0;
  padding: 0 var(--s-7);
  border-bottom: 1px solid var(--rule-soft);
  background: var(--bg);
}
.fn-tab {
  background: transparent; border: 0;
  border-bottom: 2px solid transparent;
  padding: var(--s-3) var(--s-5);
  font-family: var(--font-body); font-size: var(--t-body);
  color: var(--ink-3);
  cursor: pointer;
  margin-bottom: -1px;
  transition: color 120ms;
}
.fn-tab:hover { color: var(--ink); }
.fn-tab.active {
  color: var(--ink); font-weight: 600;
  border-bottom-color: var(--accent);
}

/* ─── Segmented controls ───────────────────────────────────── */
.fn-seg {
  display: inline-flex;
  border: 1px solid var(--rule-soft);
  background: var(--surface);
}
.fn-seg button {
  background: transparent; border: 0;
  padding: 6px 12px;
  font-family: var(--font-mono); font-size: var(--t-caption);
  letter-spacing: 0.06em;
  color: var(--ink-3); cursor: pointer;
  border-right: 1px solid var(--rule-soft);
}
.fn-seg button:last-child { border-right: 0; }
.fn-seg button.active {
  background: var(--ink); color: var(--surface-2);
}

/* ─── Section primitive ─────────────────────────────────────── */
.fn-section {
  background: var(--surface);
  border: 1px solid var(--rule-soft);
  margin-bottom: var(--s-6);
}
.fn-section-head {
  display: flex; justify-content: space-between; align-items: flex-end;
  gap: var(--s-5);
  padding: var(--s-5) var(--s-6) var(--s-3);
  border-bottom: 1px solid var(--rule-faint);
}
.fn-section-title h2 {
  margin: var(--s-1) 0 0;
  font-size: var(--t-2xl); font-weight: 400; line-height: 1.15;
  letter-spacing: -0.005em;
}
.fn-section-title .fn-italic {
  margin: var(--s-1) 0 0;
  font-style: italic; color: var(--ink-3); font-size: var(--t-body);
  max-width: 70ch; text-wrap: pretty;
}
.fn-section-actions { display: flex; gap: var(--s-3); align-items: center; }
.fn-section-body { padding: var(--s-5) var(--s-6); }

/* ─── Buttons ─────────────────────────────────────────────── */
.fn-btn {
  display: inline-flex; align-items: center; gap: var(--s-2);
  padding: 8px 14px;
  font-family: var(--font-body); font-size: var(--t-body); font-weight: 500;
  border: 1px solid var(--ink); background: var(--surface);
  color: var(--ink); cursor: pointer;
  transition: background 120ms, color 120ms;
}
.fn-btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
.fn-btn.primary:hover { background: var(--accent-hover); border-color: var(--accent-hover); }
.fn-btn.ghost { background: transparent; }
.fn-btn.ghost:hover { background: var(--bg-tint); }
.fn-btn.ghost.danger { color: var(--accent); border-color: var(--accent); }
.fn-btn.ghost.danger:hover { background: var(--accent); color: var(--surface-2); }
.fn-link {
  background: transparent; border: 0;
  font-family: var(--font-mono); font-size: var(--t-caption);
  letter-spacing: 0.04em;
  color: var(--accent); cursor: pointer;
  padding: 0;
}
.fn-link:hover { text-decoration: underline; text-underline-offset: 3px; }

/* ─── Mono meta ──────────────────────────────────────────── */
.fn-mono-meta {
  font-family: var(--font-mono); font-size: var(--t-caption);
  letter-spacing: 0.06em; color: var(--ink-3);
}
.fn-mono-meta .fn-mono-num { color: var(--accent); font-weight: 600; }
.fn-mono-meta .fn-mono-slash { color: var(--ink-4); }
.fn-mono-meta .fn-good { color: var(--role-found); font-weight: 600; }
.fn-mono-meta .fn-bad { color: var(--accent); font-weight: 600; }
.fn-muted { color: var(--ink-4); }

/* ─── Chips ──────────────────────────────────────────────── */
.fn-chips { display: flex; flex-wrap: wrap; gap: var(--s-2); margin-top: var(--s-2); }
.fn-chip {
  padding: 3px 10px;
  font-size: var(--t-caption); letter-spacing: 0.04em;
  border: 1px solid var(--rule-soft);
  background: var(--bg-tint);
  color: var(--ink-2);
}

/* ─── Callout (pitfall etc) ──────────────────────────────── */
.fn-callout {
  padding: var(--s-4) var(--s-5);
  border-left: 3px solid var(--accent);
  background: var(--bg-tint);
}
.fn-callout .eyebrow { color: var(--accent); }
.fn-callout p { margin: var(--s-2) 0 0; color: var(--ink-2); font-size: var(--t-body); }

/* ─── Two-column row ─────────────────────────────────────── */
.fn-row.two {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--s-5);
  margin: var(--s-5) 0;
  padding: 0 var(--s-6);
}
.fn-row.two > * { margin-bottom: 0 !important; }
.fn-block { padding: var(--s-3) 0; }
.fn-stack > * + * { margin-top: var(--s-3); }

/* =============================================================
   STUDY VIEW
   ============================================================= */
.fn-study {
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
  gap: var(--s-7);
  padding: var(--s-7);
  align-items: start;
  max-width: 1400px;
  margin: 0 auto;
}

.fn-index {
  position: sticky; top: var(--s-5);
  background: var(--surface);
  border: 1px solid var(--rule-soft);
}
/* Compact dropdown shown instead of the full list on narrow screens */
.fn-index-select { display: none; align-items: center; gap: var(--s-2); padding: var(--s-3) var(--s-4); }
.fn-index-select select {
  flex: 1; min-width: 0;
  font-family: var(--font-body); font-size: var(--t-body);
  padding: 6px 8px;
  background: var(--surface); color: var(--ink);
  border: 1px solid var(--ink);
}
.fn-index-head {
  display: flex; justify-content: space-between; align-items: baseline;
  padding: var(--s-3) var(--s-4);
  border-bottom: 1px solid var(--rule-faint);
}
.fn-index-list { list-style: none; margin: 0; padding: 0; }
.fn-index-list li { border-bottom: 1px solid var(--rule-faint); }
.fn-index-list li:last-child { border-bottom: 0; }
.fn-index-row {
  display: grid;
  grid-template-columns: 32px 1fr 14px;
  gap: var(--s-3); align-items: center;
  width: 100%;
  background: transparent; border: 0;
  padding: var(--s-3) var(--s-4);
  text-align: left; cursor: pointer;
  border-left: 2px solid transparent;
  transition: background 120ms, border-color 120ms;
}
.fn-index-row:hover { background: var(--bg-tint); }
.fn-index-row.active {
  background: var(--bg-tint);
  border-left-color: var(--accent);
}
.fn-index-no {
  font-size: var(--t-2xl); color: var(--ink-4); line-height: 1;
  font-variant-numeric: tabular-nums;
}
.fn-index-row.active .fn-index-no { color: var(--accent); }
.fn-index-text { display: flex; flex-direction: column; gap: 2px; min-width: 0; }
.fn-index-text strong {
  font-family: var(--font-body); font-size: var(--t-body); font-weight: 500;
  color: var(--ink);
  overflow: hidden; text-overflow: ellipsis; white-space: nowrap;
}
.fn-index-text small {
  font-size: var(--t-micro); color: var(--ink-4);
  letter-spacing: 0.04em;
}

.fn-mark {
  width: 12px; height: 12px;
  border: 1.5px solid var(--ink-4);
  background: transparent;
}
.fn-mark.done {
  background: var(--role-found);
  border-color: var(--role-found);
}
.fn-mark.inline { display: inline-block; vertical-align: middle; }

.fn-spread { min-width: 0; }

.fn-lecture-hero {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: var(--s-5);
  align-items: end;
  padding: 0 var(--s-6) var(--s-5);
  margin-bottom: var(--s-6);
  border-bottom: 1px solid var(--rule-soft);
}
.fn-lecture-hero h2 {
  margin: var(--s-1) 0 var(--s-2);
  font-size: var(--t-4xl); font-weight: 400;
  letter-spacing: -0.02em; line-height: 1.05;
}
.fn-lecture-hero p {
  margin: 0; font-style: italic; color: var(--ink-2);
  font-size: var(--t-lg); max-width: 60ch; text-wrap: pretty;
}
.fn-lecture-hero-side {
  display: flex; flex-direction: column; align-items: flex-end; gap: var(--s-2);
}

/* Goals checklist */
.fn-goals { list-style: none; margin: 0; padding: 0; }
.fn-goals li + li { border-top: 1px dashed var(--rule-faint); }
.fn-goal-row {
  display: grid;
  grid-template-columns: 26px 70px 1fr;
  gap: var(--s-3); align-items: start;
  width: 100%; padding: var(--s-3) 0;
  background: transparent; border: 0;
  text-align: left; cursor: pointer;
}
.fn-goal-row:hover { background: var(--bg-tint); margin: 0 calc(var(--s-3) * -1); padding-left: var(--s-3); padding-right: var(--s-3); }
.fn-goal-row.mastered .fn-goal-text {
  color: var(--ink-3); text-decoration: line-through; text-decoration-color: var(--ink-4);
}
.fn-goal-id {
  font-size: var(--t-micro);
  letter-spacing: 0.06em;
  color: var(--ink-4);
  padding-top: 4px;
}
.fn-goal-text {
  font-size: var(--t-body); line-height: 1.5; color: var(--ink);
  text-wrap: pretty;
}

.fn-checkbox {
  display: inline-flex; align-items: center; justify-content: center;
  width: 20px; height: 20px;
  border: 1.5px solid var(--ink-3);
  background: var(--surface-2);
  font-family: var(--font-mono); font-size: 13px; font-weight: 700; line-height: 1;
  color: var(--accent); cursor: pointer;
  flex-shrink: 0;
  margin-top: 1px;
}
.fn-checkbox.checked {
  background: var(--accent); border-color: var(--accent); color: #fff;
}

/* Concept cards */
.fn-concept {
  border: 1px solid var(--rule-soft);
  background: var(--surface-2);
}
.fn-concept-head {
  display: flex; justify-content: space-between; align-items: baseline;
  width: 100%; padding: var(--s-3) var(--s-4);
  background: transparent; border: 0; cursor: pointer; text-align: left;
  gap: var(--s-3);
}
.fn-concept-term { display: flex; align-items: baseline; gap: var(--s-3); flex-wrap: wrap; }
.fn-concept-term strong {
  font-size: var(--t-lg); font-weight: 500;
}
.fn-concept-en {
  font-family: var(--font-mono); font-size: var(--t-caption);
  color: var(--ink-4); letter-spacing: 0.04em;
  font-style: normal;
}
.fn-concept-toggle {
  font-family: var(--font-mono); font-size: var(--t-lg);
  color: var(--ink-3);
  width: 20px; text-align: center;
}
.fn-concept-body {
  margin: 0; padding: 0 var(--s-4) var(--s-4);
  font-size: var(--t-body); color: var(--ink-2);
  font-style: italic; line-height: 1.55; text-wrap: pretty;
  border-top: 1px dashed var(--rule-faint);
  padding-top: var(--s-3);
}

/* Tools */
.fn-tool {
  display: flex; justify-content: space-between; align-items: center;
  width: 100%; padding: var(--s-3) var(--s-4);
  background: var(--surface-2); border: 1px solid var(--rule-soft);
  text-align: left; cursor: pointer;
  font-family: inherit; color: inherit;
  transition: border-color 120ms, background 120ms;
}
.fn-tool.live:hover { border-color: var(--accent); background: var(--bg-tint); }
.fn-tool.live .serif { font-size: var(--t-lg); font-weight: 500; }
.fn-tool.planned {
  cursor: default; opacity: 0.7;
  border-style: dashed;
}
.fn-tool.planned .serif { font-style: italic; color: var(--ink-3); }
.fn-tool-meta {
  font-size: var(--t-caption); color: var(--ink-3);
  letter-spacing: 0.04em;
}
.fn-tool.live .fn-tool-meta { color: var(--accent); }

/* Quiz */
.fn-quiz-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: var(--s-4);
}
.fn-quiz {
  border: 1px solid var(--rule-soft);
  background: var(--surface-2);
  padding: var(--s-4);
}
.fn-quiz-head {
  display: flex; justify-content: space-between; align-items: center;
  margin-bottom: var(--s-3);
}
.fn-quiz-prompt {
  margin: 0 0 var(--s-3);
  font-size: var(--t-lg); line-height: 1.4; text-wrap: pretty;
}
.fn-quiz-options { display: flex; flex-direction: column; gap: var(--s-2); }
.fn-quiz-opt {
  display: grid;
  grid-template-columns: 24px 1fr;
  gap: var(--s-3); align-items: start;
  padding: var(--s-3); width: 100%;
  background: var(--surface); border: 1px solid var(--rule-soft);
  text-align: left; font-family: inherit; color: inherit; font-size: var(--t-body);
  cursor: pointer;
  transition: border-color 120ms, background 120ms;
}
.fn-quiz-opt:hover:not(.correct):not(.wrong) {
  border-color: var(--ink-3); background: var(--bg-tint);
}
.fn-quiz-opt.correct {
  border-color: var(--role-found);
  background: color-mix(in srgb, var(--role-found) 14%, var(--surface));
}
.fn-quiz-opt.wrong {
  border-color: var(--accent);
  background: color-mix(in srgb, var(--accent) 14%, var(--surface));
}
.fn-quiz-letter {
  font-family: var(--font-mono); font-size: var(--t-caption);
  font-weight: 700; color: var(--ink-3);
  letter-spacing: 0.04em;
}
.fn-quiz-note {
  margin: var(--s-3) 0 0;
  padding: var(--s-3) var(--s-4);
  font-size: var(--t-body); line-height: 1.5;
  border-left: 3px solid var(--ink-3);
}
.fn-quiz-note.good { border-left-color: var(--role-found); color: var(--ink-2); }
.fn-quiz-note.bad { border-left-color: var(--accent); color: var(--ink-2); }

/* =============================================================
   GLOSSARY VIEW
   ============================================================= */
.fn-glossary { padding: var(--s-7); max-width: 1100px; margin: 0 auto; }
.fn-glossary-controls {
  display: flex; align-items: center; gap: var(--s-5);
  flex-wrap: wrap;
  margin-bottom: var(--s-5);
}
.fn-search { display: flex; flex-direction: column; gap: var(--s-1); flex: 1; min-width: 220px; }
.fn-search input {
  padding: 8px 12px;
  background: var(--surface-2); border: 1px solid var(--ink);
  font-family: var(--font-body); font-size: var(--t-body);
  color: var(--ink);
  outline: none;
}
.fn-search input:focus { border-color: var(--accent); }
.fn-letters { display: flex; flex-wrap: wrap; gap: 0; border: 1px solid var(--rule-soft); }
.fn-letters button {
  padding: 6px 10px;
  background: transparent; border: 0;
  border-right: 1px solid var(--rule-soft);
  font-family: var(--font-mono); font-size: var(--t-caption);
  color: var(--ink-3); cursor: pointer;
  letter-spacing: 0.04em;
}
.fn-letters button:last-child { border-right: 0; }
.fn-letters button.active { background: var(--ink); color: var(--surface-2); }

.fn-glossary-list { list-style: none; margin: 0; padding: 0; }
.fn-glossary-row {
  padding: var(--s-5) 0;
  border-bottom: 1px solid var(--rule-faint);
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--s-2);
}
.fn-glossary-row:first-child { padding-top: 0; }
.fn-glossary-term {
  display: flex; align-items: baseline; gap: var(--s-3);
}
.fn-glossary-term h3 {
  margin: 0; font-size: var(--t-2xl); font-weight: 500;
}
.fn-glossary-term .fn-en {
  font-size: var(--t-caption); color: var(--ink-4);
  letter-spacing: 0.04em;
}
.fn-glossary-row p {
  margin: 0; font-size: var(--t-body); line-height: 1.6;
  color: var(--ink-2); font-style: italic;
  max-width: 75ch; text-wrap: pretty;
}
.fn-glossary-links { display: flex; gap: var(--s-3); flex-wrap: wrap; margin-top: var(--s-1); }
.fn-glossary-empty { padding: var(--s-7) 0; text-align: center; color: var(--ink-4); }

/* =============================================================
   PRACTICE VIEW
   ============================================================= */
.fn-practice { padding: var(--s-7); max-width: 1280px; margin: 0 auto; }
.fn-practice-strip {
  display: flex; align-items: baseline; gap: var(--s-3);
  margin-bottom: var(--s-4);
  padding-bottom: var(--s-3);
  border-bottom: 1px dashed var(--rule-faint);
}

.fn-practice-goals { list-style: none; margin: 0; padding: 0; }
.fn-pgoal {
  display: grid;
  grid-template-columns: 24px 1fr auto;
  gap: var(--s-3); align-items: start;
  padding: var(--s-3) 0;
  border-bottom: 1px dashed var(--rule-faint);
}
.fn-pgoal.mastered .fn-pgoal-text p {
  color: var(--ink-3);
  text-decoration: line-through;
  text-decoration-color: var(--ink-4);
}
.fn-pgoal-text { display: flex; flex-direction: column; gap: 2px; min-width: 0; }
.fn-pgoal-text p { margin: 0; font-size: var(--t-body); line-height: 1.5; }
.fn-pgoal-id {
  font-size: var(--t-micro); color: var(--ink-4);
  letter-spacing: 0.06em;
}
.fn-pgoal-text small {
  font-size: var(--t-micro); color: var(--ink-4);
  letter-spacing: 0.04em; margin-top: 2px;
}

/* =============================================================
   EXAM VIEW
   ============================================================= */
.fn-exam {
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
  gap: var(--s-7);
  padding: var(--s-7);
  align-items: start;
  max-width: 1500px;
  margin: 0 auto;
}
.fn-exam-index {
  position: sticky; top: var(--s-5);
  background: var(--surface);
  border: 1px solid var(--rule-soft);
}
.fn-exam-main { min-width: 0; }
.fn-search.compact { min-width: min(280px, 100%); }
.fn-search.compact input {
  width: 100%;
  font-family: var(--font-body);
  font-size: var(--t-body);
  padding: 8px 10px;
  color: var(--ink);
  background: var(--surface);
  border: 1px solid var(--rule-soft);
}
.fn-exam-controls {
  display: flex;
  align-items: flex-end;
  justify-content: flex-end;
  gap: var(--s-3);
  flex-wrap: wrap;
}
.fn-exam-select {
  display: flex;
  flex-direction: column;
  gap: 4px;
}
.fn-exam-select select {
  min-width: 170px;
  font-family: var(--font-body);
  font-size: var(--t-body);
  padding: 8px 10px;
  color: var(--ink);
  background: var(--surface);
  border: 1px solid var(--rule-soft);
}
.fn-exam-strip {
  display: flex; align-items: baseline; justify-content: space-between;
  gap: var(--s-3);
  margin-bottom: var(--s-4);
  padding-bottom: var(--s-3);
  border-bottom: 1px dashed var(--rule-faint);
}
.fn-exam-list { display: flex; flex-direction: column; gap: var(--s-4); }
.fn-exam-card {
  border: 1px solid var(--rule-soft);
  background: var(--surface);
}
.fn-exam-card.open { border-color: var(--ink); }
.fn-exam-card-head {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: var(--s-4);
  align-items: start;
  padding: var(--s-4) var(--s-5);
  border-bottom: 1px solid var(--rule-faint);
}
.fn-exam-card-head h3 {
  margin: var(--s-1) 0 0;
  font-size: var(--t-xl);
  font-weight: 500;
  line-height: 1.25;
}
.fn-exam-card-head .fn-mono-meta {
  display: block;
  margin-top: var(--s-1);
}
.fn-exam-prompt {
  padding: var(--s-4) var(--s-5);
  color: var(--ink-2);
  background: var(--bg-tint);
  max-height: 360px;
  overflow: auto;
}
.fn-exam-prompt p,
.fn-exam-solution-text p {
  margin: 0;
  font-size: var(--t-body);
  line-height: 1.65;
  color: var(--ink-2);
  overflow-wrap: anywhere;
}
.fn-exam-prompt p + p,
.fn-exam-solution-text p + p,
.fn-exam-prompt p + .fn-exam-code,
.fn-exam-solution-text p + .fn-exam-code,
.fn-exam-code + p,
.fn-exam-artifact + p,
.fn-exam-bullets + p {
  margin-top: var(--s-3);
}
.fn-exam-bullets {
  margin: var(--s-3) 0 0;
  padding-left: var(--s-5);
  color: var(--ink-2);
  line-height: 1.6;
}
.fn-exam-code {
  margin-top: var(--s-3);
}
.fn-exam-code > div {
  max-height: 320px;
  overflow: auto;
}
.fn-exam-artifact {
  margin-top: var(--s-3);
  padding: var(--s-3) var(--s-4);
  border-left: 3px solid var(--accent);
  background: var(--surface);
}
.fn-exam-artifact p {
  margin: var(--s-2) 0;
  color: var(--ink-3);
}
.fn-exam-visual {
  margin: var(--s-3) 0 0;
  padding: var(--s-3);
  border: 1px solid var(--rule-soft);
  background: var(--surface);
  overflow-x: auto;
}
.fn-exam-visual.narrow { max-width: 720px; }
.fn-exam-visual figcaption { margin-bottom: var(--s-2); }
.fn-graph-svg {
  display: block;
  width: min(100%, 760px);
  min-width: 260px;
  height: auto;
  margin: 0 auto;
}
.fn-graph-svg path {
  fill: none;
  stroke: var(--ink);
  stroke-width: 1.6;
}
.fn-graph-svg marker path { fill: var(--ink); stroke: none; }
.fn-graph-svg .strong path {
  stroke: var(--accent);
  stroke-width: 5;
  stroke-linecap: round;
  opacity: 0.65;
}
.fn-graph-svg .dashed {
  stroke-dasharray: 7 5;
}
.fn-graph-svg .node circle {
  fill: var(--surface);
  stroke: var(--ink);
  stroke-width: 1.5;
}
.fn-graph-svg .node.highlight circle {
  fill: var(--surface-2);
  stroke-width: 3;
}
.fn-graph-svg text {
  font-family: var(--font-mono);
  font-size: 13px;
  text-anchor: middle;
  fill: var(--ink);
}
.fn-graph-svg .edge-label {
  font-size: 12px;
  paint-order: stroke;
  stroke: var(--surface);
  stroke-width: 5;
  stroke-linejoin: round;
}
.fn-graph-svg .node-note {
  font-size: 11px;
  fill: var(--ink-4);
}
.fn-visual-split {
  display: grid;
  grid-template-columns: minmax(260px, 1fr) auto;
  gap: var(--s-4);
  align-items: center;
}
.fn-visual-split .fn-exam-visual {
  margin: 0;
  border: 0;
  padding: 0;
}
.fn-matrix-wrap {
  display: flex;
  justify-content: center;
}
.fn-matrix {
  border-collapse: collapse;
  font-family: var(--font-mono);
  font-size: 14px;
  color: var(--ink);
}
.fn-matrix caption {
  caption-side: bottom;
  padding-top: var(--s-2);
  font-family: var(--font-serif);
  font-size: var(--t-body);
}
.fn-matrix th,
.fn-matrix td {
  min-width: 34px;
  height: 30px;
  padding: 4px 8px;
  text-align: center;
}
.fn-matrix tbody td {
  border: 1px solid var(--rule);
  background: var(--surface-2);
}
.fn-matrix td.blank {
  background: var(--surface);
}
.fn-choice-list {
  margin: 0;
  padding-left: var(--s-5);
  font-family: var(--font-serif);
  font-size: var(--t-lg);
  line-height: 1.8;
}
.fn-formula {
  display: grid;
  grid-template-columns: auto auto minmax(0, 1fr);
  gap: var(--s-3);
  align-items: center;
  font-family: var(--font-serif);
  font-size: var(--t-lg);
}
.fn-formula.single {
  display: block;
  text-align: center;
}
.fn-formula .lhs { white-space: nowrap; }
.fn-formula .brace {
  font-size: 4rem;
  line-height: 1;
  transform: scaleX(0.65);
}
.fn-formula .cases {
  display: grid;
  grid-template-columns: minmax(110px, auto) minmax(0, 1fr);
  gap: 6px var(--s-4);
  align-items: center;
}
.fn-formula .redacted {
  display: inline-block;
  width: 150px;
  height: 18px;
  background: var(--ink);
}
.fn-formula .redacted.short { width: 70px; }
.fn-huffman-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: var(--s-3);
}
.fn-mini-tree {
  width: 100%;
  max-width: 180px;
  margin: 0 auto;
  display: block;
}
.fn-mini-tree line {
  stroke: var(--ink);
  stroke-width: 1.4;
}
.fn-mini-tree circle,
.fn-mini-tree rect {
  fill: var(--surface);
  stroke: var(--ink);
  stroke-width: 1.3;
}
.fn-mini-tree text {
  font-family: var(--font-mono);
  font-size: 12px;
  text-anchor: middle;
  fill: var(--ink);
}
.fn-mini-tree .tree-label {
  font-family: var(--font-serif);
  font-size: 15px;
}
.fn-matching-visual {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: var(--s-4);
}
.fn-matching-visual svg {
  width: 100%;
  max-width: 280px;
  margin: 0 auto;
}
.fn-matching-visual circle {
  fill: var(--surface);
  stroke: var(--ink);
  stroke-width: 1.4;
}
.fn-matching-visual .match {
  stroke: var(--ink-3);
  stroke-width: 3.5;
  fill: none;
}
.fn-matching-visual .blocking {
  stroke: var(--accent);
  stroke-width: 5;
  fill: none;
  opacity: 0.65;
}
.fn-matching-visual text {
  font-family: var(--font-serif);
  fill: var(--ink);
}
.fn-matching-visual .caption {
  text-anchor: middle;
}
.fn-matching-visual .small {
  font-size: 13px;
}
.fn-raw-visual {
  margin: 0;
  color: var(--ink);
  font-family: var(--font-mono);
  font-size: 12px;
  line-height: 1.5;
  white-space: pre;
}
.fn-exam-solution {
  border-top: 1.5px solid var(--ink);
  background: var(--surface-2);
}
.fn-exam-solution-head {
  display: flex; justify-content: space-between; align-items: baseline;
  gap: var(--s-3);
  padding: var(--s-4) var(--s-5) 0;
}
.fn-exam-solution-text {
  padding: var(--s-3) var(--s-5) var(--s-4);
  color: var(--ink);
  max-height: 420px;
  overflow: auto;
}
.fn-exam-solution-text p { color: var(--ink); }
.fn-exam-prep {
  padding: var(--s-4) var(--s-5) var(--s-5);
  border-top: 1px dashed var(--rule-faint);
}
.fn-exam-link-row {
  display: flex; flex-wrap: wrap; gap: var(--s-3);
  margin-bottom: var(--s-4);
}
.fn-exam-prep-grid {
  display: grid;
  grid-template-columns: minmax(0, 0.9fr) minmax(0, 1.3fr) minmax(0, 0.8fr);
  gap: var(--s-5);
}
.fn-chip-list {
  display: flex;
  flex-wrap: wrap;
  gap: var(--s-2);
  margin-top: var(--s-2);
}
.fn-chip.action {
  cursor: pointer;
  font-family: var(--font-mono);
  border-color: var(--rule-soft);
  text-decoration: none;
}
.fn-chip.action:hover {
  color: var(--surface-2);
  background: var(--ink);
  border-color: var(--ink);
}
.fn-exam-terms {
  display: flex;
  flex-direction: column;
  gap: var(--s-3);
  margin-top: var(--s-2);
}
.fn-exam-term {
  padding: var(--s-3);
  border-left: 2px solid var(--accent);
  background: var(--bg-tint);
}
.fn-exam-term.compact { padding: var(--s-2) var(--s-3); }
.fn-exam-term strong {
  display: block;
  font-size: var(--t-lg);
  font-weight: 500;
}
.fn-exam-term .mono {
  display: block;
  margin-top: 2px;
  color: var(--ink-4);
  font-size: var(--t-micro);
  letter-spacing: 0.04em;
}
.fn-exam-term p {
  margin: var(--s-2) 0 0;
  color: var(--ink-2);
  line-height: 1.5;
}
.fn-exam-empty { padding: var(--s-6) 0; text-align: center; }

/* =============================================================
   PROGRESS VIEW
   ============================================================= */
.fn-progress { padding: var(--s-7); max-width: 1100px; margin: 0 auto; }
.fn-progress-bars { display: flex; flex-direction: column; gap: var(--s-5); }
.fn-bar { display: flex; flex-direction: column; gap: var(--s-2); }
.fn-bar-head {
  display: flex; justify-content: space-between; align-items: baseline;
}
.fn-bar-head .serif { font-size: var(--t-lg); font-weight: 500; }
.fn-bar-head .mono {
  font-size: var(--t-caption); color: var(--ink-3);
  letter-spacing: 0.04em;
}
.fn-bar-track {
  height: 10px;
  background: var(--surface-sunken);
  border: 1px solid var(--ink);
  position: relative;
  overflow: hidden;
}
.fn-bar-fill {
  height: 100%;
  background: var(--accent);
  transition: width 280ms var(--ease-out);
}

.fn-table {
  width: 100%;
  border-collapse: collapse;
  font-size: var(--t-body);
}
.fn-table th, .fn-table td {
  padding: var(--s-3) var(--s-4);
  text-align: left;
  border-bottom: 1px dashed var(--rule-faint);
  vertical-align: middle;
}
.fn-table thead th {
  border-bottom: 1.5px solid var(--ink);
  font-family: var(--font-mono); font-size: var(--t-micro);
  letter-spacing: 0.14em; text-transform: uppercase;
  color: var(--ink-3); font-weight: 500;
  padding-bottom: var(--s-2);
}
.fn-table tbody tr:hover { background: var(--bg-tint); }
.fn-table .mono {
  font-size: var(--t-caption);
  color: var(--ink-2); font-variant-numeric: tabular-nums;
}
.fn-table td.serif { font-size: var(--t-body); }

/* =============================================================
   VISUALIZER PAGE — wrapper only; legacy app.css handles internals
   ============================================================= */
.fn-visualizer { padding: var(--s-5) var(--s-7); max-width: 1500px; margin: 0 auto; }
.fn-vis-shell {
  background: var(--surface);
  border: 1px solid var(--rule-soft);
}
.fn-vis-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: var(--s-5);
  padding: var(--s-5);
}
.fn-vis-stage { display: flex; flex-direction: column; gap: var(--s-4); min-width: 0; }
.fn-vis-side {
  display: flex; flex-direction: column; gap: var(--s-4);
  font-size: var(--t-body);
}

/* The catalogue dropdown only appears on narrow screens (see media query). */
.cat-select { display: none; align-items: center; min-width: 0; }
.cat-select select {
  flex: 1; min-width: 0;
  font-family: var(--font-body); font-size: var(--t-body);
  padding: 6px 8px;
  background: var(--surface); color: var(--ink);
  border: 1px solid var(--ink);
}

/* =============================================================
   Responsive
   ============================================================= */

/* ── Tablet / small laptop ───────────────────────────────────── */
@media (max-width: 960px) {
  .fn-study { grid-template-columns: 1fr; }
  .fn-exam { grid-template-columns: 1fr; }
  .fn-index { position: static; }
  .fn-exam-index { position: static; }
  .fn-row.two { grid-template-columns: 1fr; }
  .fn-exam-prep-grid { grid-template-columns: 1fr; }
  .fn-vis-grid { grid-template-columns: 1fr; }
  .fn-masthead { grid-template-columns: 1fr; }
  .fn-mast-controls { grid-column: 1; grid-row: auto; }
}

/* ── Phones ──────────────────────────────────────────────────── */
@media (max-width: 720px) {
  /* Never let anything push the page sideways — keep sections centred */
  html, body { overflow-x: hidden; }
  .app-shell, .fn-section, .fn-section-body, .fn-section-head,
  .fn-row, .fn-study, .fn-exam, .fn-lecture-detail, .fn-lecture-hero { min-width: 0; max-width: 100%; }
  /* Auto-fit grids with a fixed min track (e.g. minmax(300px,1fr)) overflow
     on phones narrower than that track — drop them to one column. */
  .fn-quiz-grid { grid-template-columns: 1fr; }
  /* Break genuinely-too-long words / code tokens instead of overflowing */
  .fn-section :where(h1, h2, h3, p, li, td, code, pre),
  .fn-italic, .fn-tagline, .fn-mono-meta { overflow-wrap: break-word; }

  /* Page wrappers — phone-sized gutters (were var(--s-7) = 32px each side) */
  .fn-study, .fn-glossary, .fn-practice, .fn-exam, .fn-progress { padding: var(--s-4) var(--s-3); }
  .fn-study, .fn-exam { gap: var(--s-4); }
  .fn-glossary-empty { padding: var(--s-6) 0; }

  /* Wide content scrolls inside its own box rather than into the page gutter */
  .fn-table, .fn-section-body table { display: block; width: 100%; overflow-x: auto; }
  .fn-section-body > *, .fn-section-head > *, .fn-vis-side > * { min-width: 0; }
  .fn-search { min-width: 0; flex-basis: 100%; }

  /* App shell header: tabs scroll horizontally instead of overflowing */
  .fn-masthead { padding: var(--s-4) var(--s-4) 0; gap: var(--s-2) var(--s-4); }
  .fn-mast-title h1 { font-size: var(--t-2xl); }
  .fn-mast-title .fn-tagline { font-size: var(--t-body); }
  .fn-tabs {
    margin: var(--s-4) calc(var(--s-4) * -1) 0;
    padding: 0 var(--s-4);
    flex-wrap: nowrap; overflow-x: auto; -webkit-overflow-scrolling: touch;
    scrollbar-width: none;
  }
  .fn-tabs::-webkit-scrollbar { display: none; }
  .fn-tab { white-space: nowrap; flex: 0 0 auto; padding: var(--s-3) var(--s-4); }
  .fn-mast-controls { flex-wrap: wrap; gap: var(--s-2); margin-bottom: var(--s-3); }

  /* Section primitives: tighter padding, allow head to wrap */
  .fn-section-head { padding: var(--s-4) var(--s-4) var(--s-3); flex-wrap: wrap; gap: var(--s-3); }
  .fn-section-body { padding: var(--s-4); }
  .fn-section-actions { flex-wrap: wrap; }

  /* Lecture list → dropdown (the full list ate too much vertical space) */
  .fn-index, .fn-exam-index { position: static; border: 0; margin-bottom: var(--s-4); }
  .fn-index-head, .fn-index-list { display: none; }
  .fn-index-select { display: flex; border: 1px solid var(--rule-soft); }

  /* Exam cards */
  .fn-exam-strip { flex-direction: column; align-items: flex-start; }
  .fn-exam-controls { width: 100%; justify-content: stretch; }
  .fn-exam-controls > * { flex: 1 1 100%; }
  .fn-exam-select select { width: 100%; }
  .fn-exam-card-head { grid-template-columns: 1fr; padding: var(--s-4); }
  .fn-exam-card-head .fn-btn { justify-content: center; }
  .fn-exam-prompt,
  .fn-exam-solution-text,
  .fn-exam-prep,
  .fn-exam-solution-head { padding-left: var(--s-4); padding-right: var(--s-4); }
  .fn-visual-split { grid-template-columns: 1fr; }
  .fn-formula { grid-template-columns: 1fr; gap: var(--s-2); }
  .fn-formula .brace { display: none; }
  .fn-formula .cases { grid-template-columns: 1fr; }

  /* Lecture hero: stack title and the "mark complete" button (was 1fr auto,
     which pushed the button off-screen on narrow viewports) */
  .fn-lecture-hero { grid-template-columns: 1fr; gap: var(--s-4); padding: 0 var(--s-4) var(--s-4); }
  .fn-lecture-hero h2 { font-size: var(--t-2xl); }
  .fn-lecture-hero p { font-size: var(--t-body); }
  .fn-lecture-hero-side { align-items: stretch; }
  .fn-lecture-hero-side .fn-btn { justify-content: center; }

  /* Visualizer page */
  .fn-visualizer { padding: var(--s-4) var(--s-3); }
  .fn-vis-grid { padding: var(--s-3); gap: var(--s-4); }

  /* Catalogue bar → stacked; swap tab strip for the dropdown */
  .catalogue-bar { grid-template-columns: 1fr !important; padding: var(--s-3) var(--s-4) !important; gap: var(--s-3) !important; }
  .cat-tabs { display: none !important; }
  .cat-select { display: flex !important; }
  .cat-controls { flex-wrap: wrap; }
  .cat-controls input[type="range"] { flex: 1; min-width: 90px; }

  /* Visualizer masthead ("Field Notes for X") — compact, single column */
  .vm-masthead { grid-template-columns: 1fr !important; gap: var(--s-3) !important; padding: var(--s-4) var(--s-4) var(--s-3) !important; }
  .vm-masthead h1 { font-size: var(--t-2xl) !important; }
  .vm-masthead h1 + span { font-size: var(--t-lg) !important; }
  .vm-stats { flex-wrap: wrap !important; justify-content: flex-start !important; gap: var(--s-3) var(--s-5) !important; }

  /* Transport (playback controls) — stack the three groups */
  .vis-transport { grid-template-columns: 1fr !important; gap: var(--s-3) !important; padding: var(--s-3) var(--s-3) !important; }
  .vis-transport input[type="range"] { flex: 1; min-width: 90px; }

  /* Make wide tables scroll rather than blow out the layout */
  .fn-table-wrap, .fn-section-body table { display: block; max-width: 100%; overflow-x: auto; }

  /* Larger tap targets for the small key-cap buttons */
  .fn-seg button, .cat-tab { min-height: 36px; }
}

/* ── Very small phones ───────────────────────────────────────── */
@media (max-width: 420px) {
  .fn-mast-title h1 { font-size: var(--t-xl); }
  .vm-masthead h1 { font-size: var(--t-xl) !important; }
  .vm-stats { font-size: var(--t-micro) !important; }
  .fn-section-body, .fn-section-head { padding-left: var(--s-3); padding-right: var(--s-3); }
  .fn-lecture-hero { padding-left: var(--s-3); padding-right: var(--s-3); }
  .fn-lecture-hero h2 { font-size: var(--t-xl); }
}