/* ===== RESET & BASE ===== */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --navy: #1a2332;
  --blue: #3b6fd4;
  --blue-light: #e8eef8;
  --blue-mid: #5b8dd9;
  --yellow-bg: #fef9e7;
  --yellow-border: #e8c84a;
  --border: #d1d9e6;
  --text: #1a2332;
  --text-muted: #6b7a99;
  --white: #ffffff;
  --correct: #2e7d32;
  --incorrect: #c62828;
  --canvas-bg: #f7f9fc;
  --radius: 8px;
}

body {
  font-family: 'Segoe UI', system-ui, sans-serif;
  background: #eef1f7;
  color: var(--text);
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ===== APP SHELL ===== */
#app {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* ===== HEADER ===== */
header {
  background: var(--navy);
  color: white;
  padding: 12px 28px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-shrink: 0;
}

header .module-title { font-size: 1.1rem; font-weight: 700; letter-spacing: 0.02em; }
header .screen-label { font-size: 0.78rem; color: #8fa4c8; letter-spacing: 0.08em; text-transform: uppercase; }

#voiceBtn {
  background: none;
  border: 1.5px solid #4a6fa5;
  border-radius: 6px;
  color: white;
  cursor: pointer;
  font-size: 1.2rem;
  padding: 3px 10px;
  margin-left: auto;
  transition: background 0.15s;
}
#voiceBtn:hover { background: rgba(255,255,255,0.12); }
#voiceBtn.muted { opacity: 0.45; }

/* ===== SCREEN CONTAINER ===== */
.screen {
  display: none;
  flex: 1;
  padding: 20px 24px;
  flex-direction: column;
  gap: 14px;
}
.screen.active { display: flex; }

.screen-title {
  font-size: 1.5rem;
  font-weight: 700;
  color: var(--navy);
  border-bottom: 2px solid var(--border);
  padding-bottom: 8px;
}

/* ===== THREE-COLUMN LAYOUT ===== */
.cols {
  display: grid;
  grid-template-columns: 300px 1fr 280px;
  gap: 16px;
  flex: 1;
  min-height: 0;
}

/* ===== PANELS ===== */
.panel {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px;
  overflow-y: auto;
}

.panel-label {
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  color: var(--text-muted);
  text-transform: uppercase;
  margin-bottom: 12px;
}

.panel h2 { font-size: 1.1rem; margin-bottom: 10px; }
.panel h3 { font-size: 0.95rem; margin-bottom: 8px; }
.panel p  { font-size: 0.87rem; line-height: 1.6; color: #374563; margin-bottom: 10px; }

/* ===== FORMULA BOX ===== */
.formula-box {
  background: var(--canvas-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 12px 16px;
  font-style: italic;
  font-size: 1rem;
  text-align: center;
  margin: 10px 0;
  color: var(--blue);
  font-weight: 600;
}

/* ===== INSIGHT BOX ===== */
.insight-box {
  background: var(--yellow-bg);
  border: 1px solid var(--yellow-border);
  border-radius: 6px;
  padding: 12px;
  font-size: 0.84rem;
  font-style: italic;
  color: #5a4000;
  margin-top: 10px;
}
.insight-box .insight-label {
  font-weight: 700; font-style: normal; letter-spacing: 0.08em;
  font-size: 0.7rem; text-transform: uppercase; color: #7a5a00; margin-bottom: 4px;
}

/* ===== UNIT TAGS ===== */
.unit-tags { display: flex; gap: 8px; margin: 8px 0; }
.unit-tag {
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 5px 14px;
  font-size: 0.82rem;
  background: var(--blue-light);
  color: var(--navy);
  cursor: pointer;
  transition: all 0.15s;
}
.unit-tag.active { background: var(--blue); color: white; border-color: var(--blue); }

/* ===== CANVAS PANEL ===== */
.canvas-panel {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 12px;
  position: relative;
}

canvas {
  display: block;
  border-radius: 4px;
  background: var(--canvas-bg);
  cursor: crosshair;
}

.canvas-hint {
  font-size: 0.78rem;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 6px;
}

.readout-bar {
  display: flex;
  gap: 12px;
  width: 100%;
}

.readout-chip {
  flex: 1;
  background: var(--navy);
  color: white;
  border-radius: 6px;
  padding: 8px 14px;
  font-size: 0.88rem;
  text-align: center;
  font-weight: 600;
}

/* ===== LIVE READOUT BOX ===== */
.live-readout {
  background: var(--canvas-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 12px 16px;
  width: 100%;
  font-size: 0.88rem;
  line-height: 1.8;
}
.live-readout .val { color: var(--blue); font-weight: 700; }

/* ===== RIGHT PANEL ===== */
.right-panel {
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.interactive-box {
  background: var(--blue-light);
  border: 1px solid #b8cef0;
  border-radius: var(--radius);
  padding: 14px;
}
.interactive-box .ibox-label {
  font-size: 0.7rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--blue);
  display: flex;
  align-items: center;
  gap: 6px;
  margin-bottom: 10px;
}
.interactive-box .ibox-label::before { content: "⚡"; }
.interactive-box ul { list-style: disc; padding-left: 16px; font-size: 0.82rem; line-height: 1.8; color: #2a4080; }

/* ===== CONTROLS BOX ===== */
.controls-box {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 14px;
  transition: border-color 0.35s, box-shadow 0.35s;
}
.controls-box.narration-highlight {
  border: 2.5px solid #3b6fd4;
  background: #eef3fc;
  box-shadow: 0 0 0 5px #3b6fd455, 0 4px 22px #3b6fd448;
}
.controls-box .ctrl-label {
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: 10px;
}

/* ===== UNITS SECTION HIGHLIGHT ===== */
.units-section {
  border: 2px solid transparent;
  border-radius: var(--radius);
  padding: 6px 8px;
  margin: 4px -8px 0;
  transition: border-color 0.35s, box-shadow 0.35s, background 0.35s;
}
.units-section.narration-highlight {
  border-color: #3b6fd4;
  background: #eef3fc;
  box-shadow: 0 0 0 5px #3b6fd455, 0 4px 22px #3b6fd448;
}

/* ===== SLIDER ===== */
.slider-group { margin-bottom: 14px; }
.slider-group label { font-size: 0.82rem; color: var(--text-muted); display: block; margin-bottom: 4px; }
.slider-group input[type=range] {
  width: 100%;
  accent-color: var(--blue);
  height: 4px;
  cursor: pointer;
}
.slider-val { font-size: 0.8rem; color: var(--text-muted); text-align: right; margin-top: 2px; }

/* ===== TOGGLE GROUP ===== */
.toggle-group { display: flex; gap: 6px; flex-wrap: wrap; }
.toggle-btn {
  flex: 1;
  padding: 7px 10px;
  border: 1px solid var(--border);
  border-radius: 6px;
  font-size: 0.8rem;
  background: var(--white);
  color: var(--text);
  cursor: pointer;
  transition: all 0.15s;
  text-align: center;
}
.toggle-btn:hover { border-color: var(--blue); color: var(--blue); }
.toggle-btn.active { background: var(--blue-light); border-color: var(--blue); color: var(--blue); font-weight: 600; }

/* ===== COMPARISON BOX ===== */
.comparison-box {
  background: var(--canvas-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 10px 14px;
  font-size: 0.83rem;
  line-height: 1.8;
}
.comparison-box .cv { color: var(--blue); font-weight: 700; }

/* ===== NAVIGATION ===== */
.nav-row {
  display: flex;
  gap: 10px;
  justify-content: flex-end;
  margin-top: auto;
}

.btn {
  padding: 10px 24px;
  border-radius: 6px;
  font-size: 0.88rem;
  font-weight: 600;
  cursor: pointer;
  border: 2px solid var(--navy);
  background: var(--white);
  color: var(--navy);
  transition: all 0.15s;
  letter-spacing: 0.04em;
}
.btn:hover { background: var(--navy); color: white; }
.btn.primary { background: var(--navy); color: white; }
.btn.primary:hover { background: #2d3f5c; }
.btn.reset { border-color: var(--text-muted); color: var(--text-muted); }
.btn.reset:hover { background: var(--text-muted); color: white; }

/* ===== FOOTER ===== */
footer {
  background: var(--navy);
  color: #8fa4c8;
  padding: 8px 28px;
  font-size: 0.75rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-shrink: 0;
}

/* ===== PROGRESS DOTS ===== */
.progress-dots { display: flex; gap: 6px; align-items: center; }
.dot {
  width: 8px; height: 8px; border-radius: 50%;
  background: #3a4f6e;
  transition: background 0.2s;
  cursor: pointer;
}
.dot.active { background: #5b8dd9; }
.dot.done { background: #3b6fd4; }

/* ===== SIGN CONVENTION ===== */
.sign-box {
  background: var(--canvas-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 12px;
  margin-top: 10px;
}
.sign-row {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 0.85rem;
  margin-bottom: 4px;
}
.odot  { color: #2196f3; font-size: 1.1rem; }
.otimes { color: #e53935; font-size: 1.1rem; }
.sign-lbl { color: var(--blue); font-weight: 600; }
.sign-arrow { color: var(--text-muted); }

/* ===== SCREEN 5: GRAPH PANEL ===== */
.graph-panel {
  display: flex;
  flex-direction: column;
  gap: 10px;
  width: 100%;
}

.graph-label { font-size: 0.75rem; color: var(--text-muted); margin-bottom: 2px; }

/* ===== SCREEN 6: MULTI-REP ===== */
.three-cols {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 16px;
  flex: 1;
  min-height: 0;
}

.rep-panel {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 14px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 10px;
}
.rep-panel .rep-label {
  font-size: 0.68rem;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-muted);
  font-weight: 700;
  align-self: flex-start;
}

.challenge-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}

.challenge-panel {
  background: var(--blue-light);
  border: 1px solid #b8cef0;
  border-radius: var(--radius);
  padding: 14px;
  transition: border-color 0.35s, box-shadow 0.35s;
}
.challenge-panel.narration-highlight {
  border-color: #3b6fd4;
  box-shadow: 0 0 0 5px #3b6fd455, 0 4px 22px #3b6fd448;
  animation: challengePulse 1.1s ease-in-out infinite alternate;
}
@keyframes challengePulse {
  from { box-shadow: 0 0 0 3px #3b6fd435, 0 2px 10px #3b6fd428; }
  to   { box-shadow: 0 0 0 7px #3b6fd468, 0 6px 28px #3b6fd458; }
}
.challenge-panel .ch-label {
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--blue);
  margin-bottom: 6px;
}
.challenge-panel p { font-size: 0.82rem; font-style: italic; margin-bottom: 10px; }

.choice-grid { display: flex; gap: 8px; }
.choice-item {
  flex: 1;
  background: var(--white);
  border: 2px solid var(--border);
  border-radius: 6px;
  padding: 6px;
  cursor: pointer;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  transition: all 0.15s;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-muted);
}
.choice-item:hover { border-color: var(--blue); color: var(--blue); }
.choice-item.selected { border-color: var(--blue); background: var(--blue-light); color: var(--blue); }
.choice-item.correct { border-color: var(--correct); background: #e8f5e9; color: var(--correct); }
.choice-item.wrong { border-color: var(--incorrect); background: #ffebee; color: var(--incorrect); }

/* ===== SCREEN 7-8: MCQ ===== */
.mcq-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  flex: 1;
}

.question-panel {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.q-label { font-size: 0.68rem; font-weight: 700; letter-spacing: 0.12em; text-transform: uppercase; color: var(--text-muted); }
.q-num { color: var(--blue); font-weight: 700; font-size: 1rem; }
.q-text { font-size: 0.92rem; line-height: 1.6; }

.q-formula-box {
  background: var(--canvas-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 12px 16px;
  font-size: 1rem;
  font-style: italic;
  text-align: center;
  color: var(--navy);
  font-weight: 600;
}

.q-hint {
  background: var(--yellow-bg);
  border: 1px solid var(--yellow-border);
  border-radius: 6px;
  padding: 8px 12px;
  font-size: 0.82rem;
  color: #5a4000;
}

.choices { display: flex; flex-direction: column; gap: 8px; }
.choice-btn {
  width: 100%;
  padding: 12px 16px;
  border: 1.5px solid var(--border);
  border-radius: 6px;
  background: var(--white);
  text-align: left;
  font-size: 0.88rem;
  cursor: pointer;
  transition: all 0.15s;
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.choice-btn:hover:not(:disabled) { border-color: var(--blue); background: var(--blue-light); }
.choice-btn.chosen-correct { border-color: var(--correct); background: #e8f5e9; color: var(--correct); font-weight: 600; }
.choice-btn.chosen-wrong { border-color: var(--incorrect); background: #ffebee; color: var(--incorrect); }
.choice-btn.reveal-correct { border-color: var(--correct); background: #e8f5e9; color: var(--correct); }
.choice-btn:disabled { cursor: default; }
.checkmark { font-size: 1rem; }

.solution-panel {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.sol-label { font-size: 0.68rem; font-weight: 700; letter-spacing: 0.12em; text-transform: uppercase; color: var(--text-muted); }

.sol-step {
  margin-bottom: 10px;
}
.sol-step .step-title { font-size: 0.72rem; font-weight: 700; letter-spacing: 0.1em; text-transform: uppercase; color: var(--text-muted); margin-bottom: 6px; }
.sol-step .step-formula {
  background: var(--canvas-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 10px 14px;
  font-style: italic;
  text-align: center;
  font-size: 0.92rem;
  color: var(--navy);
}

.answer-box {
  background: var(--blue-light);
  border: 1.5px solid var(--blue);
  border-radius: 6px;
  padding: 16px;
  text-align: center;
  font-size: 1.1rem;
  font-weight: 700;
  color: var(--blue);
}

.answer-label { font-size: 0.68rem; font-weight: 700; letter-spacing: 0.12em; text-transform: uppercase; color: var(--text-muted); margin-bottom: 6px; }

/* ===== UNIT SECTION LABEL ===== */
.section-label {
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin: 8px 0 4px;
}

/* ===== UNIT CONVERTER ===== */
.converter-box {
  background: var(--white);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 14px;
}
.converter-row {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-top: 8px;
}
.converter-row input[type=number] {
  flex: 1;
  padding: 8px 10px;
  border: 1.5px solid var(--border);
  border-radius: 6px;
  font-size: 0.9rem;
  text-align: center;
  outline: none;
  color: var(--navy);
}
.converter-row input[type=number]:focus { border-color: var(--blue); }
.swap-btn {
  background: none;
  border: none;
  font-size: 1.1rem;
  cursor: pointer;
  color: var(--blue);
  padding: 4px;
}
.converter-lbl { font-size: 0.78rem; color: var(--text-muted); }

/* ===== SCROLLBAR ===== */
::-webkit-scrollbar { width: 5px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: #c8d4e8; border-radius: 4px; }

/* ===== RESPONSIVE ===== */
@media (max-width: 900px) {
  .cols { grid-template-columns: 1fr; }
  .three-cols { grid-template-columns: 1fr; }
  .mcq-layout { grid-template-columns: 1fr; }
  .challenge-row { grid-template-columns: 1fr; }
}

/* S5 comparison panel styles */
.comp-uniform {
  background: var(--blue-light);
  border: 1.5px solid var(--blue);
  border-radius: 6px;
  padding: 12px;
  margin-bottom: 8px;
}
.comp-uniform .cu-label { font-size: 0.68rem; font-weight: 700; letter-spacing: 0.1em; text-transform: uppercase; color: var(--blue); margin-bottom: 6px; }

.comp-nonuniform {
  background: var(--yellow-bg);
  border: 1.5px solid var(--yellow-border);
  border-radius: 6px;
  padding: 12px;
  margin-bottom: 8px;
}
.comp-nonuniform .cnu-label { font-size: 0.68rem; font-weight: 700; letter-spacing: 0.1em; text-transform: uppercase; color: #7a5a00; margin-bottom: 6px; }

.alpha-box {
  background: var(--canvas-bg);
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 10px;
  margin-top: 6px;
}
.alpha-box .al-label { font-size: 0.68rem; font-weight: 700; letter-spacing: 0.1em; text-transform: uppercase; color: var(--text-muted); margin-bottom: 4px; }