/* ============================================================
   Duolingo-style palette
   ============================================================ */
:root {
  --bg: #131f24;
  --panel: #202f36;
  --panel-2: #2a3a42;
  --card: #37464f;
  --text: #f1f7fb;
  --muted: #afafaf;
  --border: #37464f;

  --green: #58cc02;
  --green-dark: #46a302;
  --green-glow: rgba(88, 204, 2, 0.2);
  --blue: #1cb0f6;
  --blue-dark: #1798d8;
  --orange: #ff9600;
  --red: #ff4b4b;
  --red-dark: #c33;
  --gold: #ffc800;
  --purple: #ce82ff;

  --radius: 16px;
  --radius-lg: 20px;
  --radius-sm: 10px;

  --font: "Nunito", "DIN Round", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
  font-weight: 500;
}

button, input {
  font-family: inherit;
}

/* ============================================================
   Header — chunky, playful
   ============================================================ */
header {
  padding: 1rem 1.5rem;
  border-bottom: 2px solid var(--border);
  position: sticky;
  top: 0;
  background: var(--bg);
  z-index: 10;
}

.header-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
  max-width: 1200px;
  margin: 0 auto;
}

header h1 {
  margin: 0;
  font-size: 1.4rem;
  font-weight: 800;
  letter-spacing: -0.02em;
}
.subtitle {
  margin: 0.15rem 0 0;
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  flex: 1;
  justify-content: flex-end;
  min-width: 300px;
}

#searchInput {
  flex: 1;
  max-width: 320px;
  background: var(--panel);
  border: 2px solid var(--border);
  color: var(--text);
  padding: 0.6rem 1rem;
  border-radius: var(--radius);
  font-size: 0.9rem;
  font-weight: 600;
  transition: border-color 0.15s, background 0.15s;
}
#searchInput::placeholder { color: var(--muted); font-weight: 500; }
#searchInput:focus {
  outline: none;
  border-color: var(--blue);
  background: var(--panel-2);
}

/* Duolingo "3D pressable" buttons */
.chip {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  background: var(--panel);
  border: 2px solid var(--border);
  padding: 0.45rem 0.85rem;
  border-radius: var(--radius);
  font-weight: 800;
  font-size: 0.95rem;
}

.streak {
  background: var(--panel);
  border: 2px solid var(--border);
  color: var(--muted);
  padding: 0.45rem 0.8rem;
  border-radius: var(--radius);
  font-weight: 800;
  font-size: 0.95rem;
  display: flex;
  align-items: center;
  gap: 0.3rem;
}
.streak.active {
  color: var(--orange);
  border-color: var(--orange);
  background: rgba(255, 150, 0, 0.1);
}
.streak.active::before { content: "🔥"; }
.streak:not(.active)::before { content: "❄️"; filter: grayscale(0.5); }
.streak .label { display: none; }

#xpChip {
  color: var(--gold);
  border-color: var(--gold);
  background: rgba(255, 200, 0, 0.1);
}
#xpChip::before { content: "⭐"; }

.review-btn {
  background: var(--green);
  color: #fff;
  border: none;
  border-bottom: 4px solid var(--green-dark);
  padding: 0.55rem 1.1rem;
  border-radius: var(--radius);
  cursor: pointer;
  font-weight: 800;
  font-size: 0.9rem;
  letter-spacing: 0.02em;
  text-transform: uppercase;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  transition: transform 0.05s, border-bottom-width 0.05s, filter 0.15s;
}
.review-btn:hover { filter: brightness(1.08); }
.review-btn:active {
  transform: translateY(2px);
  border-bottom-width: 2px;
}
.review-btn .badge {
  background: rgba(0,0,0,0.25);
  color: #fff;
  border-radius: 999px;
  padding: 0.1rem 0.55rem;
  font-size: 0.78rem;
  font-weight: 800;
  min-width: 1.4em;
  text-align: center;
}
.review-btn.no-due {
  background: var(--panel-2);
  color: var(--muted);
  border-bottom-color: var(--border);
}

/* ============================================================
   Category nav — pill tabs
   ============================================================ */
nav {
  display: flex;
  gap: 0.5rem;
  padding: 0.75rem 1.5rem;
  background: var(--panel);
  border-bottom: 2px solid var(--border);
  overflow-x: auto;
  scrollbar-width: none;
}
nav::-webkit-scrollbar { display: none; }

nav button {
  background: var(--panel-2);
  color: var(--text);
  border: 2px solid var(--border);
  border-bottom: 3px solid var(--border);
  padding: 0.45rem 1rem;
  border-radius: var(--radius);
  cursor: pointer;
  font-size: 0.88rem;
  font-weight: 700;
  white-space: nowrap;
  transition: transform 0.05s, filter 0.15s;
}
nav button:hover { filter: brightness(1.12); }
nav button:active { transform: translateY(1px); border-bottom-width: 2px; }
nav button.active {
  background: var(--blue);
  color: #fff;
  border-color: var(--blue);
  border-bottom-color: var(--blue-dark);
}

/* ============================================================
   Layout
   ============================================================ */
main {
  display: grid;
  grid-template-columns: 300px 1fr;
  gap: 1.25rem;
  padding: 1.25rem 1.5rem;
  min-height: calc(100vh - 220px);
  max-width: 1200px;
  margin: 0 auto;
}

/* ============================================================
   Sidebar
   ============================================================ */
#lessonList {
  background: var(--panel);
  border: 2px solid var(--border);
  border-radius: var(--radius);
  padding: 0.9rem;
  height: fit-content;
  position: sticky;
  top: 110px;
  max-height: calc(100vh - 140px);
  overflow-y: auto;
}
#lessonList h3 {
  margin: 0 0 0.6rem;
  font-size: 0.8rem;
  text-transform: uppercase;
  color: var(--muted);
  letter-spacing: 0.08em;
  font-weight: 800;
}
#lessonList .cat-group { margin-bottom: 1rem; }
#lessonList ul { list-style: none; padding: 0; margin: 0; }
#lessonList li {
  padding: 0.6rem 0.85rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.92rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 0.4rem;
  font-weight: 600;
  border: 2px solid transparent;
  margin-bottom: 0.2rem;
  transition: background 0.1s, border-color 0.1s;
}
#lessonList li:hover {
  background: var(--panel-2);
  border-color: var(--border);
}
#lessonList li.active {
  background: var(--blue);
  color: #fff;
  border-color: var(--blue);
  font-weight: 800;
}
#lessonList li .meta {
  display: flex;
  gap: 0.3rem;
  align-items: center;
  font-size: 0.78rem;
  font-weight: 800;
}
#lessonList li .check { color: var(--green); }
#lessonList li .due { color: var(--orange); }
#lessonList li.active .check,
#lessonList li.active .due { color: #fff; }

/* ============================================================
   Lesson view
   ============================================================ */
#lessonView {
  background: var(--panel);
  border: 2px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 2rem 2.25rem;
  min-height: 400px;
}

#lessonView .placeholder {
  color: var(--muted);
  text-align: center;
  padding: 4rem 1rem;
  font-size: 1.1rem;
  font-weight: 600;
}

#lessonView h2 {
  margin-top: 0;
  margin-bottom: 0.5rem;
  color: var(--text);
  font-size: 1.75rem;
  font-weight: 800;
  letter-spacing: -0.02em;
}
#lessonView h3 {
  color: var(--blue);
  margin-top: 1.75rem;
  font-size: 1.1rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}
#lessonView p { color: var(--text); }
#lessonView strong { color: var(--text); font-weight: 800; }
#lessonView ul, #lessonView ol { padding-left: 1.4rem; }
#lessonView li { margin-bottom: 0.3rem; }

#lessonView code {
  background: var(--card);
  padding: 0.15rem 0.45rem;
  border-radius: 6px;
  font-size: 0.85em;
  color: var(--gold);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-weight: 700;
}
#lessonView pre {
  background: #0f1a1f;
  padding: 1rem 1.2rem;
  border-radius: var(--radius-sm);
  overflow-x: auto;
  border: 2px solid var(--border);
  font-size: 0.86rem;
}
#lessonView pre code {
  background: none;
  padding: 0;
  color: var(--text);
  font-weight: 500;
}

#lessonView table {
  width: 100%;
  border-collapse: separate;
  border-spacing: 0;
  margin: 1rem 0;
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  overflow: hidden;
}
#lessonView th, #lessonView td {
  text-align: left;
  padding: 0.6rem 0.85rem;
  border-bottom: 1px solid var(--border);
}
#lessonView tr:last-child td { border-bottom: none; }
#lessonView th {
  color: #fff;
  background: var(--panel-2);
  font-weight: 800;
  font-size: 0.82rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
#lessonView td { font-size: 0.92rem; }

.sources {
  margin-top: 2rem;
  padding: 1rem 1.2rem;
  border-top: 2px solid var(--border);
  font-size: 0.88rem;
  color: var(--muted);
  background: var(--panel-2);
  border-radius: var(--radius-sm);
}
.sources strong { color: var(--text); }
.sources a { color: var(--blue); text-decoration: none; font-weight: 700; }
.sources a:hover { text-decoration: underline; }

/* ============================================================
   Quiz — Duolingo-style cards
   ============================================================ */
.complete-gate {
  margin: 1.25rem 0;
  padding: 0.85rem 1rem;
  background: rgba(255, 150, 0, 0.1);
  border: 2px solid var(--orange);
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  color: var(--orange);
  font-weight: 700;
}

.quiz {
  margin-top: 2rem;
  background: var(--panel-2);
  padding: 1.5rem;
  border-radius: var(--radius);
  border: 2px solid var(--border);
}
.quiz h3 {
  margin-top: 0;
  color: var(--text);
  font-size: 1.1rem;
  font-weight: 800;
  letter-spacing: -0.01em;
}
.quiz .q {
  margin-bottom: 1.75rem;
  padding-bottom: 1.25rem;
  border-bottom: 2px dashed var(--border);
}
.quiz .q:last-child {
  border-bottom: none;
  margin-bottom: 0;
  padding-bottom: 0;
}
.quiz .q > p {
  font-weight: 700;
  font-size: 1rem;
  margin: 0 0 0.75rem;
  color: var(--text);
}

.srs-chip {
  display: inline-block;
  font-size: 0.7rem;
  padding: 0.15rem 0.55rem;
  border-radius: 999px;
  margin-left: 0.45rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  background: var(--panel);
  color: var(--muted);
  border: 1px solid var(--border);
}
.srs-chip.new { background: rgba(28, 176, 246, 0.15); color: var(--blue); border-color: var(--blue); }
.srs-chip.due { background: rgba(255, 150, 0, 0.15); color: var(--orange); border-color: var(--orange); }
.srs-chip.ok { background: rgba(88, 204, 2, 0.15); color: var(--green); border-color: var(--green); }

/* MC options — big 3D buttons */
.quiz .opt {
  display: flex;
  align-items: center;
  width: 100%;
  text-align: left;
  background: var(--panel);
  border: 2px solid var(--border);
  border-bottom: 4px solid var(--border);
  color: var(--text);
  padding: 0.85rem 1rem;
  border-radius: var(--radius);
  margin-bottom: 0.5rem;
  cursor: pointer;
  font-size: 0.95rem;
  font-weight: 700;
  transition: transform 0.05s, filter 0.1s;
}
.quiz .opt:hover:not(:disabled) {
  filter: brightness(1.1);
  border-color: var(--blue);
}
.quiz .opt:active:not(:disabled) {
  transform: translateY(2px);
  border-bottom-width: 2px;
}
.quiz .opt:disabled { cursor: default; opacity: 0.65; }
.quiz .opt .key-hint {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 1.9em;
  height: 1.9em;
  padding: 0 0.3em;
  border: 2px solid var(--border);
  border-radius: 8px;
  font-size: 0.75rem;
  color: var(--muted);
  margin-right: 0.7rem;
  font-family: ui-monospace, monospace;
  font-weight: 800;
  flex-shrink: 0;
}

.quiz .opt.correct {
  background: var(--green-glow);
  border-color: var(--green);
  border-bottom-color: var(--green-dark);
  color: var(--green);
  animation: pulse-green 0.5s;
}
.quiz .opt.correct .key-hint { border-color: var(--green); color: var(--green); }
.quiz .opt.wrong {
  background: rgba(255, 75, 75, 0.15);
  border-color: var(--red);
  border-bottom-color: var(--red-dark);
  color: var(--red);
  animation: shake 0.45s;
}
.quiz .opt.wrong .key-hint { border-color: var(--red); color: var(--red); }

.quiz .explain {
  margin-top: 0.75rem;
  padding: 0.85rem 1rem;
  font-size: 0.9rem;
  color: var(--text);
  border-left: 4px solid var(--blue);
  background: var(--panel);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  font-weight: 600;
}

/* Fill-in */
.fill-input {
  width: 100%;
  background: var(--panel);
  border: 2px solid var(--border);
  border-bottom: 4px solid var(--border);
  color: var(--text);
  padding: 0.75rem 1rem;
  border-radius: var(--radius);
  font-size: 1rem;
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
  font-weight: 600;
}
.fill-input:focus {
  outline: none;
  border-color: var(--blue);
  border-bottom-color: var(--blue-dark);
}
.fill-input.correct {
  border-color: var(--green);
  border-bottom-color: var(--green-dark);
  background: var(--green-glow);
  animation: pulse-green 0.5s;
}
.fill-input.wrong {
  border-color: var(--red);
  border-bottom-color: var(--red-dark);
  background: rgba(255, 75, 75, 0.15);
  animation: shake 0.45s;
}
.fill-submit {
  margin-top: 0.5rem;
  padding: 0.6rem 1.25rem;
  background: var(--blue);
  color: #fff;
  border: none;
  border-bottom: 4px solid var(--blue-dark);
  border-radius: var(--radius);
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  cursor: pointer;
  font-size: 0.85rem;
  transition: transform 0.05s, filter 0.1s;
}
.fill-submit:hover { filter: brightness(1.1); }
.fill-submit:active { transform: translateY(2px); border-bottom-width: 2px; }
.fill-submit:disabled { opacity: 0.55; cursor: default; }
.fill-hint {
  font-size: 0.78rem;
  color: var(--muted);
  margin-top: 0.35rem;
  font-style: italic;
  font-weight: 600;
}

/* ============================================================
   Review mode — focus card
   ============================================================ */
.review-card {
  background: var(--panel-2);
  padding: 2rem;
  border-radius: var(--radius-lg);
  border: 2px solid var(--border);
}
.review-progress {
  display: flex;
  gap: 0.75rem;
  align-items: center;
  color: var(--muted);
  font-size: 0.85rem;
  margin-bottom: 1.25rem;
  font-weight: 700;
}
.review-progress .bar {
  flex: 1;
  height: 14px;
  background: var(--panel);
  border: 2px solid var(--border);
  border-radius: 999px;
  overflow: hidden;
}
.review-progress .bar > div {
  background: linear-gradient(90deg, var(--green) 0%, var(--blue) 100%);
  height: 100%;
  transition: width 0.3s ease;
  border-radius: 999px;
}
#exitReviewBtn {
  background: var(--panel);
  border: 2px solid var(--border);
  border-bottom: 3px solid var(--border);
  color: var(--muted);
  padding: 0.4rem 0.8rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-family: inherit;
  font-size: 0.78rem;
  font-weight: 800;
  text-transform: uppercase;
}
#exitReviewBtn:hover { filter: brightness(1.1); }

.review-card .context {
  font-size: 0.85rem;
  color: var(--muted);
  margin-bottom: 1rem;
  font-weight: 600;
}
.review-card .context a {
  color: var(--blue);
  text-decoration: none;
  font-weight: 800;
}

.lesson-context-toggle {
  margin: 1rem 0;
  background: var(--panel);
  border: 2px solid var(--border);
  border-bottom: 3px solid var(--border);
  color: var(--muted);
  padding: 0.45rem 0.9rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.82rem;
  font-weight: 800;
  text-transform: uppercase;
}
.lesson-context-toggle:hover { color: var(--blue); border-color: var(--blue); }
.lesson-context-panel {
  margin-top: 1rem;
  padding: 1.25rem;
  background: var(--panel);
  border-radius: var(--radius-sm);
  border: 2px solid var(--border);
  max-height: 400px;
  overflow-y: auto;
  font-size: 0.9rem;
}

/* ============================================================
   Complete / Next buttons
   ============================================================ */
.mark-complete {
  margin-top: 1.5rem;
  background: var(--green);
  color: #fff;
  border: none;
  border-bottom: 4px solid var(--green-dark);
  padding: 0.85rem 1.75rem;
  border-radius: var(--radius);
  cursor: pointer;
  font-weight: 800;
  font-size: 0.95rem;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  transition: transform 0.05s, filter 0.1s;
}
.mark-complete:hover { filter: brightness(1.08); }
.mark-complete:active { transform: translateY(2px); border-bottom-width: 2px; }
.mark-complete.done {
  background: var(--panel);
  color: var(--green);
  border-color: var(--green);
  border-bottom-color: var(--green-dark);
}

/* ============================================================
   Footer
   ============================================================ */
footer {
  padding: 1rem 1.5rem;
  border-top: 2px solid var(--border);
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--muted);
  font-size: 0.82rem;
  font-weight: 700;
  flex-wrap: wrap;
  gap: 0.5rem;
  max-width: 1200px;
  margin: 0 auto;
}
.footer-actions { display: flex; gap: 0.5rem; align-items: center; }
footer button {
  background: var(--panel);
  border: 2px solid var(--border);
  border-bottom: 3px solid var(--border);
  color: var(--muted);
  padding: 0.4rem 0.8rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 0.78rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}
footer button:hover { color: var(--text); filter: brightness(1.1); }
footer button:active { transform: translateY(1px); border-bottom-width: 2px; }
#resetBtn:hover { color: var(--red); border-color: var(--red); }

/* ============================================================
   Animations — celebratory feedback
   ============================================================ */
@keyframes pulse-green {
  0%   { transform: scale(1); }
  40%  { transform: scale(1.04); box-shadow: 0 0 0 10px rgba(88, 204, 2, 0.15); }
  100% { transform: scale(1); box-shadow: 0 0 0 0 transparent; }
}

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  15% { transform: translateX(-8px); }
  30% { transform: translateX(7px); }
  45% { transform: translateX(-5px); }
  60% { transform: translateX(4px); }
  75% { transform: translateX(-2px); }
}

/* ============================================================
   Daily goal bar
   ============================================================ */
.daily-goal {
  background: var(--panel);
  border-bottom: 2px solid var(--border);
  padding: 0.5rem 1.5rem;
}
.daily-goal-inner {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  gap: 0.8rem;
  font-size: 0.82rem;
  font-weight: 800;
  color: var(--muted);
}
.daily-goal .label { text-transform: uppercase; letter-spacing: 0.05em; font-size: 0.75rem; }
.daily-goal .amount { color: var(--gold); }
.daily-goal .bar {
  flex: 1;
  height: 10px;
  background: var(--bg);
  border: 2px solid var(--border);
  border-radius: 999px;
  overflow: hidden;
}
.daily-goal .bar > div {
  background: linear-gradient(90deg, var(--gold) 0%, var(--green) 100%);
  height: 100%;
  border-radius: 999px;
  transition: width 0.4s ease;
}
.daily-goal.complete .bar > div { background: var(--green); }
.daily-goal.complete .label { color: var(--green); }

/* Mute / sound toggle */
.icon-btn {
  background: var(--panel);
  border: 2px solid var(--border);
  border-bottom: 3px solid var(--border);
  color: var(--muted);
  padding: 0.45rem 0.6rem;
  border-radius: var(--radius-sm);
  cursor: pointer;
  font-size: 1rem;
  transition: filter 0.15s, transform 0.05s;
}
.icon-btn:hover { filter: brightness(1.1); color: var(--text); }
.icon-btn:active { transform: translateY(1px); border-bottom-width: 2px; }
.icon-btn.active { color: var(--blue); border-color: var(--blue); }

/* ============================================================
   Learning path / skill tree
   ============================================================ */
.unit-intro {
  background: linear-gradient(135deg, var(--blue) 0%, var(--green) 100%);
  color: #fff;
  padding: 1.75rem 2rem;
  border-radius: var(--radius-lg);
  margin-bottom: 1.5rem;
  display: flex;
  align-items: center;
  gap: 1.25rem;
  box-shadow: 0 6px 0 rgba(0, 0, 0, 0.15);
}
.unit-intro .unit-icon {
  font-size: 3rem;
  line-height: 1;
  filter: drop-shadow(0 2px 4px rgba(0,0,0,0.25));
}
.unit-intro .unit-meta { flex: 1; }
.unit-intro .unit-label {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  opacity: 0.85;
  font-weight: 800;
  margin-bottom: 0.25rem;
}
.unit-intro h2 {
  color: #fff !important;
  font-size: 1.7rem;
  margin: 0 0 0.3rem 0;
  font-weight: 800;
  letter-spacing: -0.02em;
}
.unit-intro .unit-desc {
  font-size: 0.95rem;
  opacity: 0.95;
  margin-bottom: 0.75rem;
  font-weight: 600;
}
.unit-intro .unit-progress {
  display: flex;
  gap: 0.75rem;
  font-size: 0.82rem;
  opacity: 0.95;
  font-weight: 800;
}
.unit-intro .unit-start {
  background: #fff;
  color: var(--blue);
  border: none;
  border-bottom: 4px solid rgba(0,0,0,0.2);
  padding: 0.85rem 1.5rem;
  border-radius: var(--radius);
  font-weight: 800;
  font-size: 0.95rem;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  cursor: pointer;
  transition: transform 0.05s, filter 0.15s;
  font-family: inherit;
  white-space: nowrap;
}
.unit-intro .unit-start:hover { filter: brightness(1.05); }
.unit-intro .unit-start:active { transform: translateY(2px); border-bottom-width: 2px; }

.path {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1.25rem;
  padding: 1rem 0 2rem;
}
.path-node {
  position: relative;
  width: 90px;
  height: 90px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: transform 0.1s;
  font-size: 2rem;
  font-weight: 800;
  flex-direction: column;
  gap: 0.2rem;
}
.path-node:hover { transform: scale(1.05); }
.path-node .node-title {
  position: absolute;
  top: 100%;
  margin-top: 0.5rem;
  font-size: 0.78rem;
  white-space: nowrap;
  color: var(--text);
  font-weight: 700;
  background: var(--panel-2);
  padding: 0.2rem 0.65rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  pointer-events: none;
}
.path-node.locked {
  background: var(--panel-2);
  border: 4px solid var(--border);
  border-bottom: 8px solid var(--border);
  color: var(--muted);
  cursor: not-allowed;
  opacity: 0.6;
}
.path-node.locked:hover { transform: none; }
.path-node.available {
  background: var(--blue);
  border: 4px solid var(--blue);
  border-bottom: 8px solid var(--blue-dark);
  color: #fff;
}
.path-node.current {
  background: var(--gold);
  border: 4px solid var(--gold);
  border-bottom: 8px solid #cfa700;
  color: #000;
  animation: bounce 1.5s ease-in-out infinite;
}
.path-node.done {
  background: var(--green);
  border: 4px solid var(--green);
  border-bottom: 8px solid var(--green-dark);
  color: #fff;
}
.path-node.mastered {
  background: var(--gold);
  border: 4px solid var(--gold);
  border-bottom: 8px solid #cfa700;
  color: #000;
}
.path-node.mastered::after {
  content: "⭐";
  position: absolute;
  top: -8px;
  right: -8px;
  font-size: 1.5rem;
  filter: drop-shadow(0 2px 2px rgba(0,0,0,0.3));
}

/* Zig-zag the path */
.path-node:nth-child(3n+1) { margin-left: 0; }
.path-node:nth-child(3n+2) { margin-left: 120px; }
.path-node:nth-child(3n+3) { margin-left: -120px; }
.path-node:nth-child(3n+4) { margin-left: 60px; }
.path-node:nth-child(3n+5) { margin-left: -60px; }

@keyframes bounce {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-6px); }
}

/* ============================================================
   Sequential challenge mode (Duolingo-style lesson)
   ============================================================ */
.challenge-intro {
  text-align: center;
  padding: 2.5rem 1rem;
}
.challenge-intro .big-icon { font-size: 4rem; margin-bottom: 0.5rem; }
.challenge-intro h2 {
  color: var(--text);
  font-size: 1.8rem;
  margin: 0 0 0.5rem;
  font-weight: 800;
  letter-spacing: -0.02em;
}
.challenge-intro .sub {
  color: var(--muted);
  font-size: 1rem;
  margin-bottom: 1.5rem;
  font-weight: 600;
}
.challenge-intro .start-challenge {
  background: var(--green);
  color: #fff;
  border: none;
  border-bottom: 5px solid var(--green-dark);
  padding: 1rem 2.25rem;
  border-radius: var(--radius);
  cursor: pointer;
  font-weight: 800;
  font-size: 1.05rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  transition: transform 0.05s, filter 0.1s;
  font-family: inherit;
}
.challenge-intro .start-challenge:hover { filter: brightness(1.08); }
.challenge-intro .start-challenge:active { transform: translateY(2px); border-bottom-width: 3px; }

.challenge-complete {
  text-align: center;
  padding: 3rem 1rem;
  animation: pop-in 0.5s ease-out;
}
.challenge-complete .trophy {
  font-size: 5rem;
  margin-bottom: 0.5rem;
  animation: trophy-spin 0.8s ease-out;
}
.challenge-complete h2 {
  color: var(--gold) !important;
  font-size: 2rem;
  margin: 0 0 1rem;
}
.challenge-complete .summary {
  display: flex;
  justify-content: center;
  gap: 1.5rem;
  margin: 1.5rem 0;
}
.challenge-complete .stat {
  background: var(--panel-2);
  border: 2px solid var(--border);
  border-bottom: 4px solid var(--border);
  padding: 1rem 1.5rem;
  border-radius: var(--radius);
  min-width: 110px;
}
.challenge-complete .stat .value {
  font-size: 1.8rem;
  font-weight: 800;
  color: var(--gold);
}
.challenge-complete .stat .label {
  font-size: 0.78rem;
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  font-weight: 700;
}
.challenge-complete .continue-btn {
  background: var(--green);
  color: #fff;
  border: none;
  border-bottom: 5px solid var(--green-dark);
  padding: 1rem 2.5rem;
  border-radius: var(--radius);
  font-size: 1rem;
  font-weight: 800;
  text-transform: uppercase;
  cursor: pointer;
  letter-spacing: 0.04em;
  font-family: inherit;
  margin-top: 1rem;
}
.challenge-complete .continue-btn:active { transform: translateY(2px); border-bottom-width: 3px; }

@keyframes pop-in {
  0% { opacity: 0; transform: scale(0.85); }
  100% { opacity: 1; transform: scale(1); }
}
@keyframes trophy-spin {
  0% { transform: rotate(-20deg) scale(0.5); opacity: 0; }
  50% { transform: rotate(10deg) scale(1.15); opacity: 1; }
  100% { transform: rotate(0) scale(1); opacity: 1; }
}

/* Inter-question cheer */
.cheer-msg {
  text-align: center;
  font-size: 1.1rem;
  color: var(--green);
  font-weight: 800;
  margin-top: 1rem;
  animation: cheer-pop 0.5s ease-out;
}
@keyframes cheer-pop {
  0% { opacity: 0; transform: translateY(8px); }
  100% { opacity: 1; transform: translateY(0); }
}

/* ============================================================
   Floating XP toast
   ============================================================ */
.xp-toast {
  position: fixed;
  top: 80px;
  left: 50%;
  transform: translateX(-50%) translateY(-20px);
  background: var(--gold);
  color: #000;
  padding: 0.8rem 1.6rem;
  border-radius: 999px;
  font-weight: 800;
  font-size: 1rem;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
  opacity: 0;
  pointer-events: none;
  z-index: 100;
  animation: xp-pop 1.4s ease-out forwards;
  border: 3px solid #fff;
}
@keyframes xp-pop {
  0%   { opacity: 0; transform: translateX(-50%) translateY(-20px) scale(0.6); }
  20%  { opacity: 1; transform: translateX(-50%) translateY(0) scale(1.1); }
  30%  { transform: translateX(-50%) translateY(0) scale(1); }
  85%  { opacity: 1; transform: translateX(-50%) translateY(0) scale(1); }
  100% { opacity: 0; transform: translateX(-50%) translateY(-30px) scale(0.9); }
}

/* Confetti-ish sparkle on lesson complete */
@keyframes level-up-flash {
  0%, 100% { background: var(--green); }
  50% { background: var(--gold); }
}
.mark-complete.just-completed { animation: level-up-flash 0.8s; }

/* ============================================================
   Responsive
   ============================================================ */
@media (max-width: 900px) {
  main { grid-template-columns: 1fr; padding: 1rem; }
  #lessonList { position: static; max-height: none; }
  .header-actions { width: 100%; gap: 0.4rem; }
  #searchInput { max-width: none; min-width: 140px; }
  .streak, #xpChip { padding: 0.4rem 0.6rem; font-size: 0.85rem; }
  .review-btn { padding: 0.5rem 0.85rem; font-size: 0.8rem; }
  #lessonView { padding: 1.5rem 1.25rem; }
}