:root {
  --bg: #f5f8fb;
  --panel: #ffffff;
  --ink: #13253a;
  --ink-soft: #4f647d;
  --line: #d6e1ec;
  --line-strong: #c0d2e4;
  --accent: #2d7ff9;
  --accent-2: #1bbf9a;
  --danger: #d14a4a;
  --shadow: 0 12px 30px rgba(20, 46, 73, 0.08);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Outfit", "Segoe UI", sans-serif;
  color: var(--ink);
  background:
    radial-gradient(900px 460px at 10% -10%, rgba(45, 127, 249, 0.12), transparent 60%),
    radial-gradient(900px 460px at 90% -20%, rgba(27, 191, 154, 0.13), transparent 62%),
    var(--bg);
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  gap: 14px;
  border-bottom: 1px solid var(--line);
  background: rgba(245, 248, 251, 0.9);
  backdrop-filter: blur(10px);
  padding: 14px 20px;
}

.back-btn {
  border: 1px solid var(--line-strong);
  border-radius: 10px;
  padding: 10px 13px;
  text-decoration: none;
  color: var(--ink);
  background: #fff;
  font-weight: 700;
  font-size: 14px;
}

.back-btn:hover {
  border-color: var(--accent);
}

.title-wrap h1 {
  margin: 0;
  font-size: clamp(26px, 3.4vw, 40px);
  letter-spacing: -0.02em;
}

.title-wrap p {
  margin: 4px 0 0;
  color: var(--ink-soft);
}

.app-shell {
  width: calc(100% - 16px);
  margin: 10px auto 18px;
  display: grid;
  grid-template-columns: minmax(300px, 360px) minmax(0, 1fr) minmax(280px, 360px);
  gap: 12px;
}

.card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 15px;
  box-shadow: var(--shadow);
  padding: 14px;
}

h2 {
  margin: 0;
  font-size: 22px;
}

h3 {
  margin: 0;
  font-size: 18px;
}

.controls-grid {
  margin-top: 10px;
  display: grid;
  gap: 10px;
}

label {
  display: grid;
  gap: 6px;
}

label span {
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: #597693;
  font-weight: 800;
}

.control-hint {
  color: #5c7692;
  font-size: 12px;
  line-height: 1.35;
}

input,
select,
button {
  font: inherit;
}

input,
select {
  width: 100%;
  border: 1px solid var(--line-strong);
  border-radius: 10px;
  padding: 10px 11px;
  color: var(--ink);
  background: #fff;
}

input:focus,
select:focus {
  outline: 2px solid rgba(45, 127, 249, 0.2);
  border-color: var(--accent);
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 10px;
}

.btn {
  border: 1px solid var(--line-strong);
  border-radius: 10px;
  padding: 9px 12px;
  background: #fff;
  font-size: 14px;
  font-weight: 700;
  color: #1f456a;
  cursor: pointer;
}

.btn:hover {
  border-color: var(--accent);
}

.btn.primary {
  border-color: transparent;
  color: #fff;
  background: linear-gradient(95deg, var(--accent), var(--accent-2));
}

.btn.ghost {
  border-style: dashed;
}

.switch {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 7px 11px;
  background: #f8fbff;
}

.switch input {
  width: 14px;
  height: 14px;
  margin: 0;
}

.switch span {
  font-size: 13px;
  font-weight: 700;
  color: #2c547a;
}

.status-line {
  margin: 10px 0 0;
  border: 1px solid #d5e7f9;
  border-radius: 10px;
  background: #f3f9ff;
  color: #29567e;
  padding: 10px;
  font-size: 14px;
}

.flag-pill {
  margin: 10px 0 0;
  display: inline-flex;
  align-items: center;
  width: fit-content;
  border: 1px solid #c8def8;
  background: #eef6ff;
  color: #1f5a91;
  border-radius: 999px;
  padding: 6px 10px;
  font-size: 12px;
  font-weight: 800;
  letter-spacing: 0.03em;
  text-transform: uppercase;
}

.flag-pill.flag-solvable {
  border-color: #8ad4c3;
  background: #ecfbf6;
  color: #0f7860;
}

.flag-pill.flag-unsolvable {
  border-color: #f1b0b0;
  background: #fff3f3;
  color: #a43e3e;
}

.flag-pill.flag-random {
  border-color: #d7c3fa;
  background: #f7f1ff;
  color: #5f3d9a;
}

.legend {
  margin-top: 10px;
  display: grid;
  gap: 7px;
}

.legend-item {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: #395a7b;
}

.legend-dot {
  width: 14px;
  height: 14px;
  border-radius: 50%;
  border: 2px solid rgba(255, 255, 255, 0.95);
  box-shadow: 0 0 0 1px rgba(24, 57, 89, 0.22);
}

.board-panel {
  padding: 0;
  overflow: hidden;
}

.board-head {
  padding: 12px 14px;
  border-bottom: 1px solid var(--line);
}

.board-head p {
  margin: 6px 0 0;
  color: var(--ink-soft);
  font-size: 14px;
}

.board-wrap {
  display: none;
  width: 100%;
  height: min(80vh, 900px);
  background: #0a1930;
}

.board-wrap.active {
  display: block;
}

#board-2d {
  width: 100%;
  height: 100%;
  display: block;
  touch-action: none;
  cursor: crosshair;
}

#cube-scene {
  width: 100%;
  height: 100%;
}

#cube-scene .cube-fallback {
  display: grid;
  place-items: center;
  width: 100%;
  height: 100%;
  padding: 24px;
  text-align: center;
  color: #cde2ff;
  background: linear-gradient(180deg, #0b1f3d 0%, #0a1930 100%);
  font-size: 14px;
  line-height: 1.4;
}

.meta-panel {
  display: grid;
  gap: 12px;
  align-content: start;
}

.stats-list {
  margin: 0;
  padding-left: 18px;
  display: grid;
  gap: 6px;
  color: #2d5378;
}

.math-panel {
  border: 1px solid var(--line);
  border-radius: 10px;
  background: #f9fcff;
  padding: 10px;
  display: grid;
  gap: 8px;
}

.hidden {
  display: none !important;
}

.meta-line {
  margin: 0;
  color: #355a7f;
  font-size: 13px;
}

.formula {
  font-family: "Source Sans 3", sans-serif;
  letter-spacing: 0.02em;
}

.solver-panel {
  border: 1px solid var(--line);
  border-radius: 10px;
  background: #fff;
  padding: 10px;
  display: grid;
  gap: 7px;
}

@media (max-width: 1300px) {
  .app-shell {
    grid-template-columns: 1fr;
  }

  .board-wrap {
    height: min(72vh, 760px);
  }
}