:root {
  --bg-0: #07080f;
  --bg-1: #0f1226;
  --fg: #e9ecf5;
  --fg-dim: #9aa3c0;
  --accent: #6cf2c9;
  --accent-2: #a26bff;
  --warn: #ffb454;
  --danger: #ff5577;
  --panel: rgba(15, 18, 38, 0.72);
  --panel-border: rgba(255, 255, 255, 0.08);
  --shadow: 0 10px 40px rgba(0, 0, 0, 0.45);
  --safe-top: env(safe-area-inset-top, 0px);
  --safe-bottom: env(safe-area-inset-bottom, 0px);
  --safe-left: env(safe-area-inset-left, 0px);
  --safe-right: env(safe-area-inset-right, 0px);
}

* {
  box-sizing: border-box;
  -webkit-tap-highlight-color: transparent;
}

html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  width: 100%;
  overflow: hidden;
  background: radial-gradient(ellipse at top, var(--bg-1), var(--bg-0) 70%);
  color: var(--fg);
  font-family: ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  user-select: none;
  -webkit-user-select: none;
  touch-action: none;
  overscroll-behavior: none;
}

#app {
  position: fixed;
  inset: 0;
  display: block;
}

#scene {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  display: block;
  touch-action: none;
}

.hud {
  position: absolute;
  z-index: 10;
  display: flex;
  pointer-events: none;
}

.hud > * {
  pointer-events: auto;
}

.hud.top {
  top: calc(var(--safe-top) + 12px);
  left: 0;
  right: 0;
  justify-content: center;
}

.hud-group {
  display: flex;
  gap: 10px;
  background: var(--panel);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border: 1px solid var(--panel-border);
  padding: 8px 14px;
  border-radius: 14px;
  box-shadow: var(--shadow);
}

.stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  min-width: 70px;
  padding: 0 6px;
}

.stat .label {
  font-size: 10px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--fg-dim);
}

.stat .value {
  font-variant-numeric: tabular-nums;
  font-weight: 600;
  font-size: 18px;
  margin-top: 2px;
  color: var(--fg);
}

.hud.right {
  right: calc(var(--safe-right) + 12px);
  top: 50%;
  transform: translateY(-50%);
  flex-direction: column;
  gap: 8px;
}

.hud.bottom {
  bottom: calc(var(--safe-bottom) + 12px);
  left: 0;
  right: 0;
  justify-content: center;
}

.btn {
  appearance: none;
  border: 1px solid var(--panel-border);
  background: var(--panel);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  color: var(--fg);
  padding: 10px 14px;
  border-radius: 12px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  box-shadow: var(--shadow);
  transition: transform 0.08s ease, background 0.15s ease, border-color 0.15s ease;
  min-height: 42px;
}

.btn:hover {
  border-color: rgba(255, 255, 255, 0.2);
}

.btn:active {
  transform: scale(0.96);
}

.btn .icon {
  font-size: 18px;
  line-height: 1;
  display: inline-block;
  width: 18px;
  text-align: center;
}

.btn.primary {
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #0b0d17;
  border-color: transparent;
}

.btn.big {
  padding: 14px 22px;
  font-size: 16px;
}

.btn.toggle[data-on="false"] {
  opacity: 0.55;
}
.btn.toggle[data-on="true"] {
  border-color: var(--accent);
  color: var(--accent);
}

.theme-picker {
  display: flex;
  align-items: center;
  gap: 8px;
  background: var(--panel);
  border: 1px solid var(--panel-border);
  padding: 8px 12px;
  border-radius: 12px;
  box-shadow: var(--shadow);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}

.theme-picker .label {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: 0.16em;
  color: var(--fg-dim);
  margin-right: 4px;
}

.swatch {
  width: 26px;
  height: 26px;
  border-radius: 8px;
  border: 2px solid rgba(255, 255, 255, 0.15);
  cursor: pointer;
  background: linear-gradient(135deg, #ffffff 0%, #ffffff 16.6%, #ffd400 16.6%, #ffd400 33.3%, #ff5b3a 33.3%, #ff5b3a 50%, #4cc14c 50%, #4cc14c 66.6%, #2d6cdf 66.6%, #2d6cdf 83.3%, #ff8c2a 83.3%, #ff8c2a 100%);
}

.swatch[data-theme="neon"] {
  background: linear-gradient(135deg, #ff0080, #7928ca, #2af598, #009efd, #ffe53b, #ff2525);
}
.swatch[data-theme="pastel"] {
  background: linear-gradient(135deg, #ffd1dc, #ffe5b4, #fff5ba, #b5ead7, #c7ceea, #f1c0e8);
}
.swatch[data-theme="mono"] {
  background: linear-gradient(135deg, #fff, #ddd, #aaa, #777, #444, #111);
}

.swatch.active {
  border-color: var(--accent);
  box-shadow: 0 0 0 2px rgba(108, 242, 201, 0.35);
}

.banner {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(7, 8, 15, 0.6);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: 30;
  animation: fadein 0.3s ease;
}

.banner-content {
  text-align: center;
  padding: 32px 40px;
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: 18px;
  box-shadow: var(--shadow);
}

.banner h1 {
  font-size: 48px;
  margin: 0 0 10px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  letter-spacing: 0.06em;
}

.banner p {
  margin: 0 0 18px;
  color: var(--fg-dim);
  font-size: 16px;
  line-height: 1.5;
}

.modal {
  position: absolute;
  inset: 0;
  background: rgba(7, 8, 15, 0.7);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 40;
  padding: 20px;
}

.modal-content {
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: 18px;
  padding: 24px 28px;
  max-width: 460px;
  width: 100%;
  box-shadow: var(--shadow);
}

.modal-content h2 {
  margin-top: 0;
  font-size: 22px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.modal-content ul {
  padding-left: 18px;
  line-height: 1.7;
  color: var(--fg);
}

.modal-content li strong {
  color: var(--accent);
}

.modal-content .hint {
  color: var(--fg-dim);
  font-size: 13px;
  margin: 12px 0 18px;
}

.splash {
  position: absolute;
  inset: 0;
  background: radial-gradient(ellipse at center, var(--bg-1), var(--bg-0));
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
  cursor: pointer;
  transition: opacity 0.5s ease, visibility 0.5s ease;
}

.splash-content {
  text-align: center;
  animation: pulse 2.4s ease-in-out infinite;
}

.splash h1 {
  font-size: clamp(36px, 8vw, 64px);
  margin: 0;
  letter-spacing: 0.18em;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}

.splash p {
  margin-top: 12px;
  color: var(--fg-dim);
  letter-spacing: 0.18em;
  text-transform: uppercase;
  font-size: 12px;
}

.hidden {
  display: none !important;
}

/* ---------- Tutorial panel ---------- */
.tutorial-panel {
  position: fixed;
  top: calc(var(--safe-top) + 12px);
  bottom: calc(var(--safe-bottom) + 12px);
  left: calc(var(--safe-left) + 12px);
  width: 360px;
  max-width: calc(100vw - 24px);
  background: var(--panel);
  border: 1px solid var(--panel-border);
  border-radius: 16px;
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  z-index: 25;
  animation: tut-slide-in 0.28s ease;
  overflow: hidden;
}

@keyframes tut-slide-in {
  from { transform: translateX(-16px); opacity: 0; }
  to   { transform: translateX(0); opacity: 1; }
}

.tut-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 14px;
  border-bottom: 1px solid var(--panel-border);
}

.tut-header-left {
  display: flex;
  align-items: center;
  gap: 10px;
}

.tut-badge {
  font-size: 11px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  padding: 4px 8px;
  border-radius: 6px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #0b0d17;
  font-weight: 700;
}

.tut-step-label {
  font-size: 12px;
  color: var(--fg-dim);
  letter-spacing: 0.08em;
}

.tut-close {
  appearance: none;
  background: transparent;
  border: none;
  color: var(--fg-dim);
  font-size: 18px;
  cursor: pointer;
  width: 32px;
  height: 32px;
  border-radius: 8px;
  transition: background 0.15s ease, color 0.15s ease;
}
.tut-close:hover { background: rgba(255, 255, 255, 0.06); color: var(--fg); }

.tut-progress {
  height: 3px;
  background: rgba(255, 255, 255, 0.06);
}
.tut-progress-bar {
  height: 100%;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  transition: width 0.3s ease;
  width: 0%;
}

.tut-body {
  padding: 14px 16px 4px;
  overflow-y: auto;
  flex: 1;
}

.tut-title {
  margin: 0 0 8px;
  font-size: 17px;
  color: var(--fg);
}

.tut-intro {
  margin: 0 0 14px;
  font-size: 13.5px;
  line-height: 1.55;
  color: var(--fg);
}

.tut-section-label {
  font-size: 10px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--fg-dim);
  margin: 8px 0 6px;
}

.tut-tips {
  margin: 0 0 12px;
  padding-left: 18px;
  font-size: 12.5px;
  line-height: 1.55;
  color: var(--fg);
}
.tut-tips li { margin-bottom: 4px; }

.tut-algos {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-bottom: 8px;
}

.tut-algo {
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid var(--panel-border);
  border-radius: 10px;
  padding: 10px 12px;
}

.tut-algo-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  margin-bottom: 6px;
}

.tut-algo-name {
  font-size: 13px;
  font-weight: 600;
  color: var(--fg);
}

.tut-algo-notation {
  display: block;
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  font-size: 14px;
  color: var(--accent);
  background: rgba(0, 0, 0, 0.28);
  padding: 6px 8px;
  border-radius: 6px;
  letter-spacing: 0.04em;
  word-spacing: 0.1em;
}

.tut-algo-desc {
  margin: 6px 0 0;
  font-size: 12px;
  color: var(--fg-dim);
  line-height: 1.5;
}

.tut-btn {
  appearance: none;
  border: 1px solid var(--panel-border);
  background: rgba(255, 255, 255, 0.04);
  color: var(--fg);
  padding: 7px 11px;
  border-radius: 8px;
  font-size: 12.5px;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s ease, transform 0.08s ease, border-color 0.15s ease;
}
.tut-btn:hover:not(:disabled) { border-color: rgba(255, 255, 255, 0.22); background: rgba(255, 255, 255, 0.08); }
.tut-btn:active:not(:disabled) { transform: scale(0.96); }
.tut-btn:disabled { opacity: 0.45; cursor: not-allowed; }

.tut-btn.primary {
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: #0b0d17;
  border-color: transparent;
}

.tut-algo-play {
  white-space: nowrap;
}

.tut-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  padding: 10px 14px;
  border-top: 1px solid var(--panel-border);
}

/* When the tutorial is open, nudge the side HUD a bit so it doesn't overlap on
   narrow desktops. */
body.tutorial-open .hud.top { padding-left: 360px; }

@media (max-width: 720px) {
  .tutorial-panel {
    top: auto;
    left: 0;
    right: 0;
    bottom: 0;
    width: 100%;
    max-width: none;
    max-height: 68vh;
    border-radius: 16px 16px 0 0;
  }
  body.tutorial-open .hud.top { padding-left: 0; }
  body.tutorial-open .hud.bottom { display: none; }
}

.splash.fade {
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
}

@keyframes pulse {
  0%, 100% { transform: scale(1); opacity: 1; }
  50% { transform: scale(1.04); opacity: 0.85; }
}

@keyframes fadein {
  from { opacity: 0; transform: scale(0.96); }
  to { opacity: 1; transform: scale(1); }
}

/* Mobile tweaks */
@media (max-width: 640px) {
  .btn .text {
    display: none;
  }
  .btn {
    padding: 10px;
    width: 44px;
    height: 44px;
    justify-content: center;
  }
  .hud.right {
    right: calc(var(--safe-right) + 8px);
    gap: 6px;
  }
  .hud-group {
    padding: 6px 10px;
    gap: 4px;
  }
  .stat {
    min-width: 56px;
    padding: 0 4px;
  }
  .stat .value {
    font-size: 15px;
  }
  .stat .label {
    font-size: 9px;
  }
  .theme-picker .label {
    display: none;
  }
  .banner h1 { font-size: 36px; }
}

@media (orientation: landscape) and (max-height: 480px) {
  .hud.top {
    top: calc(var(--safe-top) + 6px);
  }
  .hud.bottom {
    bottom: calc(var(--safe-bottom) + 6px);
  }
}