:root {
  --bg: #f6f7fb;
  --bg-panel: #ffffff;
  --bg-panel-2: #f1f3f9;
  --border: #e3e6ef;
  --text: #1a1d29;
  --text-dim: #6b7280;
  --accent: #6d5ef8;
  --accent-2: #a855f7;
  --shadow: 0 4px 24px rgba(30, 34, 60, 0.06);
  --shadow-lg: 0 12px 40px rgba(30, 34, 60, 0.16);

  --orange: #c2660a;
  --orange-bg: #fdedd9;
  --purple: #7c3aed;
  --purple-bg: #efe6fe;
  --grey: #5b6270;
  --grey-bg: #eceef3;
  --green: #12805c;
  --green-bg: #dbf5e9;
  --red: #d5303f;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  line-height: 1.55;
}

/* ---------- toolbar ---------- */

.toolbar {
  display: flex;
  align-items: center;
  gap: 20px;
  flex-wrap: wrap;
  padding: 16px 24px;
  background: var(--bg-panel);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
}

.brand {
  font-size: 20px;
  font-weight: 800;
  letter-spacing: -0.01em;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  white-space: nowrap;
}
.brand span { font-weight: 800; }

.toolbar-controls {
  display: flex;
  align-items: center;
  gap: 12px;
  flex-wrap: wrap;
}

.toolbar-links {
  margin-left: auto;
  display: flex;
  gap: 12px;
  font-size: 18px;
}
.toolbar-links a { text-decoration: none; opacity: 0.7; }
.toolbar-links a:hover { opacity: 1; }

.hero {
  max-width: 720px;
  margin: 36px auto 8px;
  padding: 0 24px;
  text-align: center;
}
.hero-title {
  font-size: clamp(22px, 3.4vw, 30px);
  font-weight: 750;
  line-height: 1.35;
  margin: 0 0 20px;
  letter-spacing: -0.01em;
}
.hero-chart {
  margin: 0 auto 14px;
  max-width: 480px;
}
.hero-chart svg { width: 100%; height: auto; display: block; }
.hero-curve {
  stroke-dasharray: 500;
  stroke-dashoffset: 500;
  animation: diagDraw 1.1s ease forwards;
}
.hero-caption {
  color: var(--text-dim);
  font-size: 13px;
  margin: 0;
}

.control {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 12px;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.control select {
  background: var(--bg-panel);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 8px 12px;
  font-size: 14px;
  min-width: 180px;
  box-shadow: var(--shadow);
}

.control-big select {
  font-size: 16px;
  font-weight: 700;
  padding: 11px 16px;
  min-width: 220px;
  border-width: 1.5px;
  border-radius: 10px;
}

.times {
  color: var(--text-dim);
  font-size: 16px;
}

/* ---------- main layout ---------- */

main {
  max-width: 1200px;
  margin: 0 auto;
  padding: 24px 24px 80px;
}

.explorer { margin-top: 8px; }

/* ---------- stage: the hero diagram + interact bar ---------- */

.stage {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 18px;
  box-shadow: var(--shadow-lg);
  padding: 24px;
  margin-bottom: 20px;
}

.interact-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
  align-items: flex-start;
  margin-bottom: 18px;
  padding-bottom: 18px;
  border-bottom: 1px solid var(--border);
}
.interact-bar > * { flex: 1; min-width: 260px; }

.stage-diagram-wrap {
  position: relative;
}
.stage-badge-corner {
  display: none; /* the diagram's own topbar badge already shows tier; this stays available for future use */
}
.stage-diagram .diagram-wrap {
  background: var(--bg-panel-2);
  border-radius: 14px;
  padding: 18px 18px 8px;
  margin-bottom: 0;
}
.stage-diagram .diagram-caption {
  font-size: 14px;
  max-width: 720px;
  margin-left: auto;
  margin-right: auto;
}
.stage-diagram svg text { font-size: 15px; }
.stage-diagram .anim-draw { stroke-width: 3; }

.panels {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
}

@media (max-width: 760px) {
  .panels { grid-template-columns: 1fr; }
}

.panel {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 22px;
  min-height: 220px;
  box-shadow: var(--shadow);
}

.panel-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 14px;
}

.panel-header h2 {
  font-size: 13px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-dim);
  margin: 0;
  font-weight: 700;
}

.evidence-tag {
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  padding: 4px 10px;
  border-radius: 999px;
  white-space: nowrap;
}

.evidence-tag.orange { color: var(--orange); background: var(--orange-bg); }
.evidence-tag.purple { color: var(--purple); background: var(--purple-bg); }
.evidence-tag.grey { color: var(--grey); background: var(--grey-bg); }
.evidence-tag.green { color: var(--green); background: var(--green-bg); }

.diagram-wrap {
  position: relative;
  background: var(--bg-panel-2);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 10px 6px 4px;
  margin-bottom: 16px;
}
.diagram-wrap svg {
  display: block;
  margin: 0 auto;
  width: auto;
  height: auto;
  max-width: 100%;
  max-height: 460px;
}
.diagram-wrap .diag-node { cursor: help; }
.diagram-wrap .diag-node rect, .diagram-wrap .diag-node circle { transition: filter 0.15s ease; }
.diagram-wrap .diag-node:hover rect, .diagram-wrap .diag-node:hover circle { filter: brightness(1.06) saturate(1.15); }

.diagram-topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  margin-bottom: 4px;
}
.diagram-badge {
  font-size: 10px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  padding: 3px 9px;
  border-radius: 999px;
}
.diagram-badge.real { color: var(--orange); background: var(--orange-bg); }
.diagram-badge.illustrative { color: var(--grey); background: var(--grey-bg); }
.diagram-badge.live { color: var(--green); background: var(--green-bg); animation: diagPulse 1.6s ease-in-out infinite; }

.diagram-replay {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  color: var(--text-dim);
  border-radius: 999px;
  padding: 4px 10px;
  font-size: 11px;
  cursor: pointer;
}
.diagram-replay:hover { color: var(--text); border-color: var(--accent); }
.diagram-caption {
  font-size: 12px;
  color: var(--text-dim);
  text-align: center;
  margin: 4px 6px 8px;
}
.diagram-raw {
  margin: 0 6px 10px;
  font-size: 12px;
}
.diagram-raw summary {
  cursor: pointer;
  color: var(--accent);
  font-weight: 600;
}
.diagram-raw pre {
  white-space: pre-wrap;
  word-break: break-word;
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 10px;
  margin-top: 6px;
  max-height: 220px;
  overflow-y: auto;
  font-size: 11.5px;
  color: var(--text-dim);
}

.question-picker {
  padding: 12px 14px;
  background: var(--bg-panel-2);
  border: 1px solid var(--border);
  border-radius: 10px;
  font-size: 12px;
  color: var(--text-dim);
}
.question-picker label {
  font-size: 12px;
  font-weight: 600;
  color: var(--text);
  display: block;
  margin-bottom: 8px;
}
.live-controls {
  margin-bottom: 14px;
  padding: 14px 16px;
  background: var(--green-bg);
  border: 1.5px solid var(--green);
  border-radius: 12px;
}
.live-controls-row {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  align-items: center;
  margin-bottom: 10px;
}
.live-controls-row input[type="text"] {
  flex: 1;
  min-width: 260px;
  background: var(--bg-panel);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 8px;
  padding: 9px 12px;
  font-size: 13px;
}
.live-controls-row input[type="range"] {
  flex: 1;
  min-width: 160px;
  accent-color: var(--green);
}
.live-slider-label {
  font-size: 12px;
  font-weight: 700;
  color: var(--green);
  white-space: nowrap;
  min-width: 150px;
}
.live-controls button {
  background: var(--green);
  color: #fff;
  border: none;
  border-radius: 8px;
  padding: 10px 18px;
  font-size: 13px;
  font-weight: 700;
  cursor: pointer;
}
.live-controls button:disabled {
  background: var(--grey);
  cursor: not-allowed;
}
.live-hint {
  margin-top: 6px;
  font-size: 12px;
  color: var(--text-dim);
  min-height: 16px;
}

.live-sample-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  gap: 12px;
  margin: 12px 0;
}
.live-sample-card {
  background: var(--bg-panel);
  border: 1.5px solid var(--border);
  border-radius: 10px;
  padding: 10px;
  transition: border-color 0.2s ease;
}
.live-sample-card.done { border-color: var(--text-dim); }
.live-sample-card.winner { border-color: var(--green); background: var(--green-bg); }
.live-sample-label {
  font-size: 11px;
  font-weight: 700;
  color: var(--text-dim);
  text-transform: uppercase;
  letter-spacing: 0.03em;
  margin-bottom: 6px;
}
.live-sample-text {
  font-family: ui-monospace, "SF Mono", Consolas, monospace;
  font-size: 11.5px;
  line-height: 1.5;
  color: var(--text);
  white-space: pre-wrap;
  word-break: break-word;
  max-height: 140px;
  overflow-y: auto;
  margin: 0 0 6px;
}
.live-sample-status {
  font-size: 11px;
  color: var(--text-dim);
  font-weight: 600;
}
.live-sample-status.active { color: var(--green); }
.live-sample-status.active::before { content: "● "; animation: diagPulse 1s ease-in-out infinite; }

.live-vote-box {
  margin-top: 10px;
  padding: 10px 14px;
  background: var(--purple-bg);
  border: 1px solid var(--purple);
  border-radius: 8px;
  font-size: 13px;
  font-weight: 600;
  color: var(--purple);
}

.live-timeline { margin: 12px 0; }
.live-segment { margin-bottom: 10px; }
.live-wait-marker {
  font-size: 11px;
  font-weight: 700;
  color: var(--orange);
  background: var(--orange-bg);
  border-radius: 999px;
  padding: 4px 10px;
  display: inline-block;
  margin-bottom: 10px;
}

.question-picker select {
  width: 100%;
  background: var(--bg-panel);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 8px;
  padding: 8px 10px;
  font-size: 13px;
}

.anim-fade {
  opacity: 0;
  animation: diagFadeIn 0.5s ease forwards;
}
@keyframes diagFadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: translateY(0); }
}

.anim-draw {
  stroke-dasharray: 260;
  stroke-dashoffset: 260;
  animation: diagDraw 0.6s ease forwards;
}
@keyframes diagDraw {
  to { stroke-dashoffset: 0; }
}

.winner-pulse {
  animation: diagFadeIn 0.5s ease forwards, diagPulse 1.4s ease-in-out 1.1s infinite;
}
@keyframes diagPulse {
  0%, 100% { filter: drop-shadow(0 0 0 rgba(74, 222, 128, 0)); }
  50% { filter: drop-shadow(0 0 6px rgba(74, 222, 128, 0.55)); }
}

.prune-fade {
  animation: diagFadeIn 0.5s ease forwards, diagPruneFade 0.5s ease forwards 1.2s;
}
@keyframes diagPruneFade {
  to { opacity: 0.35; }
}

.blocked-x {
  animation: diagFadeIn 0.5s ease forwards, diagShake 0.4s ease 1s;
}
@keyframes diagShake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-3px); }
  75% { transform: translateX(3px); }
}

.panel-body p { margin: 0 0 12px; }
.panel-body .equation {
  font-family: "Cambria Math", Cambria, serif;
  font-size: 16px;
  background: var(--bg-panel-2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 10px 14px;
  margin: 8px 0;
}
.panel-body .equation .note {
  display: block;
  font-family: -apple-system, sans-serif;
  font-size: 11px;
  color: var(--text-dim);
  margin-top: 4px;
}

.panel-body .quote {
  border-left: 3px solid var(--accent);
  padding-left: 12px;
  color: var(--text-dim);
  font-style: italic;
  margin: 12px 0;
}

.panel-body .beat { margin-bottom: 16px; }
.panel-body .beat h4 { margin: 0 0 4px; font-size: 14px; }

.no-data {
  color: var(--text-dim);
  border: 1px dashed var(--border);
  background: var(--bg-panel-2);
  border-radius: 10px;
  padding: 16px;
  font-size: 14px;
}
.no-data + .no-data { margin-top: 14px; }
.no-data .evidence-tag { margin-bottom: 8px; display: inline-block; }

.blocked-banner {
  color: var(--red);
  font-weight: 700;
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 10px;
}

.slider-block { margin-top: 16px; }
.slider-block input[type="range"] {
  width: 100%;
  accent-color: var(--accent);
}
.slider-value {
  display: flex;
  justify-content: space-between;
  font-size: 12px;
  color: var(--text-dim);
  margin-bottom: 6px;
}

.chart-wrap { margin: 12px 0; }
.chart-wrap svg { width: 100%; height: auto; display: block; }
.chart-axis-label { fill: var(--text-dim); font-size: 10px; }
.chart-line {
  fill: none;
  stroke: var(--accent);
  stroke-width: 2.5;
  stroke-dasharray: 500;
  stroke-dashoffset: 500;
  animation: diagDraw 0.8s ease forwards;
}
.chart-point { fill: var(--accent); cursor: pointer; transition: r 0.15s ease; }
.chart-point:hover { r: 6; }
.chart-point.current { fill: var(--red); r: 5; }
.chart-fill { fill: url(#chartGradient); opacity: 0.5; }

.per-problem-detail {
  margin-top: 14px;
  border-top: 1px solid var(--border);
  padding-top: 12px;
  font-size: 13px;
}
.per-problem-detail .row {
  display: flex;
  justify-content: space-between;
  gap: 8px;
  padding: 4px 0;
}
.per-problem-detail .correct { color: var(--green); font-weight: 600; }
.per-problem-detail .incorrect { color: var(--red); font-weight: 600; }

.task-toggle { display: flex; gap: 8px; margin-bottom: 12px; }
.task-toggle button {
  background: var(--bg-panel-2);
  border: 1px solid var(--border);
  color: var(--text-dim);
  border-radius: 999px;
  padding: 6px 14px;
  font-size: 12px;
  cursor: pointer;
}
.task-toggle button.active {
  color: #fff;
  border-color: var(--accent);
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
}

.bdh-strip {
  margin-top: 16px;
  padding: 16px 20px;
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  box-shadow: var(--shadow);
  font-size: 13px;
  color: var(--text-dim);
}
.bdh-strip strong { color: var(--text); }
.bdh-strip .equation { font-family: Cambria, serif; color: var(--text); margin-top: 6px; }

.panel-body { transition: opacity 0.14s ease; }

.failure-moment, .final-challenge {
  margin-top: 48px;
  padding-top: 32px;
  border-top: 1px solid var(--border);
  opacity: 0;
  transform: translateY(18px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}
.failure-moment.in-view, .final-challenge.in-view {
  opacity: 1;
  transform: translateY(0);
}
.failure-moment h2, .final-challenge h2 { font-size: 20px; margin-bottom: 16px; }

.stat-table { width: 100%; border-collapse: collapse; font-size: 13px; margin: 12px 0; background: var(--bg-panel); }
.stat-table th, .stat-table td { border: 1px solid var(--border); padding: 8px 10px; text-align: left; }
.stat-table th { color: var(--text-dim); font-weight: 600; background: var(--bg-panel-2); }

.challenge-choices { display: flex; gap: 10px; margin: 12px 0; flex-wrap: wrap; }
.challenge-choices button {
  background: var(--bg-panel);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 8px;
  padding: 10px 16px;
  cursor: pointer;
  box-shadow: var(--shadow);
}
.challenge-choices button.selected {
  border-color: var(--accent);
  background: var(--purple-bg);
  color: var(--purple);
}
.challenge-reveal {
  margin-top: 16px;
  padding: 16px;
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 10px;
}
.challenge-reveal[hidden] { display: none; }

textarea.free-text {
  width: 100%;
  min-height: 90px;
  background: var(--bg-panel);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 8px;
  padding: 10px;
  font-family: inherit;
  font-size: 14px;
  resize: vertical;
}

footer {
  max-width: 1040px;
  margin: 0 auto;
  padding: 24px 24px 60px;
  color: var(--text-dim);
  font-size: 13px;
}
footer h3 { color: var(--text); font-size: 14px; }
footer ul { padding-left: 18px; }
footer li { margin-bottom: 8px; }

/* ---------- floating tutorial card ---------- */

.tutorial-card {
  position: fixed;
  bottom: 24px;
  right: 24px;
  width: 340px;
  max-width: calc(100vw - 32px);
  background: var(--bg-panel);
  border: 1px solid var(--border);
  border-radius: 16px;
  box-shadow: var(--shadow-lg);
  padding: 20px 22px;
  z-index: 100;
}
.tutorial-card[hidden] { display: none; }

.tutorial-close {
  position: absolute;
  top: 12px;
  right: 14px;
  background: none;
  border: none;
  font-size: 18px;
  color: var(--text-dim);
  cursor: pointer;
  line-height: 1;
}

.tutorial-card h3 {
  margin: 0 0 10px;
  font-size: 16px;
  color: var(--accent);
}
.tutorial-card p {
  margin: 0;
  font-size: 13px;
  color: var(--text-dim);
  line-height: 1.6;
}

.tutorial-nav {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 14px;
  margin-top: 16px;
}
.tutorial-nav button {
  width: 30px;
  height: 30px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: var(--bg-panel-2);
  color: var(--accent);
  font-size: 16px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
}
.tutorial-nav button:hover { background: var(--purple-bg); }
#tutorial-index { font-size: 12px; color: var(--text-dim); min-width: 36px; text-align: center; }