:root {
  --bg: #f3f5f8;
  --bg-soft: #eef2f7;
  --panel: rgba(255, 255, 255, .92);
  --panel-solid: #ffffff;
  --text: #111827;
  --muted: #657287;
  --line: #dfe5ee;
  --line-strong: #cbd5e1;
  --accent: #1d4ed8;
  --accent-hover: #1e40af;
  --accent-soft: rgba(29, 78, 216, .10);
  --accent-2: #0f766e;
  --accent-2-soft: rgba(15, 118, 110, .10);
  --danger: #dc2626;
  --ok: #16a34a;
  --warning: #b45309;
  --light-square: #efe7dc;
  --dark-square: #826f59;
  --select: #f59e0b;
  --legal: rgba(29, 78, 216, .38);
  --capture: rgba(220, 38, 38, .45);
  --shadow: 0 14px 42px rgba(15, 23, 42, .08);
  --shadow-sm: 0 8px 22px rgba(15, 23, 42, .06);
  --shadow-lg: 0 24px 70px rgba(15, 23, 42, .16);
  --radius: 20px;
  --radius-sm: 14px;
  --font-sans: ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", "Noto Sans SC", sans-serif;
  --font-mono: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  color-scheme: light;
}

* { box-sizing: border-box; }
html, body { min-height: 100%; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font-sans);
  color: var(--text);
  background:
    radial-gradient(circle at 14% 8%, rgba(29, 78, 216, .14), transparent 30rem),
    radial-gradient(circle at 88% 4%, rgba(15, 118, 110, .13), transparent 24rem),
    linear-gradient(180deg, #f8fafc 0%, var(--bg) 46%, #eef2f7 100%);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
body::before {
  content: "";
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  opacity: .52;
  background-image: linear-gradient(rgba(15,23,42,.035) 1px, transparent 1px), linear-gradient(90deg, rgba(15,23,42,.035) 1px, transparent 1px);
  background-size: 34px 34px;
}
button, input, select, textarea { font: inherit; }
button {
  border: 0;
  border-radius: 999px;
  padding: .72rem 1.08rem;
  color: #fff;
  background: linear-gradient(135deg, var(--accent), #2563eb);
  cursor: pointer;
  font-weight: 750;
  font-size: .92rem;
  letter-spacing: .01em;
  transition: transform .16s ease, box-shadow .18s ease, opacity .16s ease, background .18s ease;
  box-shadow: 0 10px 20px rgba(29, 78, 216, .20);
}
button:hover { transform: translateY(-1px); box-shadow: 0 14px 26px rgba(29, 78, 216, .25); }
button:active { transform: translateY(0); box-shadow: 0 6px 14px rgba(29, 78, 216, .18); }
button:disabled { opacity: .45; cursor: not-allowed; transform: none; box-shadow: none; }
button.secondary {
  color: #1f2937;
  background: #f8fafc;
  box-shadow: none;
  border: 1px solid var(--line);
}
button.secondary:hover { background: #eef2ff; border-color: #bfdbfe; box-shadow: var(--shadow-sm); }
button.danger { background: linear-gradient(135deg, var(--danger), #ef4444); box-shadow: 0 10px 20px rgba(220, 38, 38, .20); }
button.ok { background: linear-gradient(135deg, var(--ok), #22c55e); box-shadow: 0 10px 20px rgba(22, 163, 74, .20); }
button.ghost {
  color: var(--accent);
  background: transparent;
  border: 1px solid var(--line-strong);
  box-shadow: none;
}
button.ghost:hover { background: var(--accent-soft); border-color: #93c5fd; }
input, select, textarea {
  width: 100%;
  border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm);
  background: #fff;
  padding: .76rem .9rem;
  color: var(--text);
  outline: none;
  transition: border-color .18s ease, box-shadow .18s ease, background .18s ease;
  font-size: .94rem;
}
input:focus, select:focus, textarea:focus { border-color: var(--accent); box-shadow: 0 0 0 4px rgba(29,78,216,.10); }
textarea { min-height: 7rem; resize: vertical; }
label { display: grid; gap: .38rem; font-weight: 750; color: #374151; font-size: .9rem; }
small, .small { color: var(--muted); line-height: 1.55; font-size: .85rem; }

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  gap: 1rem;
  align-items: center;
  justify-content: space-between;
  padding: .95rem clamp(1rem, 4vw, 3.3rem);
  background: rgba(255,255,255,.82);
  backdrop-filter: blur(22px);
  -webkit-backdrop-filter: blur(22px);
  border-bottom: 1px solid rgba(203,213,225,.76);
  box-shadow: 0 8px 26px rgba(15, 23, 42, .04);
}
.brand { display: flex; gap: .85rem; align-items: center; cursor: pointer; user-select: none; }
.brand-mark {
  display: grid;
  place-items: center;
  width: 3rem;
  height: 3rem;
  border-radius: 16px;
  color: #fff;
  background: linear-gradient(135deg, #0f172a, #1d4ed8 52%, #0f766e);
  box-shadow: 0 14px 28px rgba(29,78,216,.24);
  font-size: 1.62rem;
}
.brand h1 { margin: 0; font-size: clamp(1.08rem, 2vw, 1.42rem); letter-spacing: .015em; font-weight: 900; }
.brand p { margin: .12rem 0 0; color: var(--muted); font-size: .82rem; }
.top-nav { display: flex; gap: .5rem; flex-wrap: wrap; justify-content: flex-end; }
.top-nav button { padding: .58rem .85rem; font-size: .88rem; border-radius: 999px; }

.app-shell { width: min(1280px, calc(100% - 1.6rem)); margin: 1.5rem auto 3rem; }
.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.18fr) minmax(300px, .82fr);
  gap: 1.2rem;
  align-items: stretch;
}
.card, .panel {
  position: relative;
  background: var(--panel);
  border: 1px solid rgba(203, 213, 225, .88);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  overflow: hidden;
}
.card::after, .panel::after {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  border-radius: inherit;
  box-shadow: inset 0 1px 0 rgba(255,255,255,.82);
}
.card { padding: clamp(1.2rem, 2.5vw, 2.4rem); }
.hero-card { min-height: 430px; display: grid; align-content: center; }
.hero-eyebrow { display: flex; flex-wrap: wrap; gap: .55rem; align-items: center; margin-bottom: 1rem; }
.hero-title { font-size: clamp(2.05rem, 4.7vw, 4.55rem); line-height: 1.02; margin: 0 0 1rem; letter-spacing: -.045em; font-weight: 950; }
.hero-title span { color: var(--accent); }
.hero-copy { color: var(--muted); font-size: 1.02rem; line-height: 1.78; margin: 0 0 1.35rem; }
.action-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: .72rem; }
.feature-list { display: grid; gap: .72rem; margin-top: 1.15rem; }
.feature { display: flex; gap: .65rem; align-items: flex-start; color: #374151; line-height: 1.58; font-size: .93rem; }
.feature b { color: var(--accent); font-weight: 850; }
.feature-dot { flex: 0 0 auto; width: .72rem; height: .72rem; border-radius: 50%; margin-top: .42rem; background: linear-gradient(135deg, var(--accent), var(--accent-2)); box-shadow: 0 0 0 4px rgba(29,78,216,.10); }
.badge {
  display: inline-flex;
  align-items: center;
  gap: .34rem;
  border-radius: 999px;
  padding: .34rem .72rem;
  background: var(--accent-2-soft);
  color: var(--accent-2);
  border: 1px solid rgba(15,118,110,.16);
  font-weight: 850;
  font-size: .82rem;
  letter-spacing: .01em;
}
.badge.official { background: #fff7ed; color: #9a3412; border-color: #fed7aa; }
.stat-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: .75rem; margin-top: .2rem; }
.stat-card { padding: 1rem; border: 1px solid var(--line); border-radius: var(--radius-sm); background: rgba(248,250,252,.72); }
.stat-card strong { display: block; font-size: 1.45rem; line-height: 1; margin-bottom: .28rem; }
.stat-card span { color: var(--muted); font-size: .84rem; }
.official-note {
  padding: .95rem 1rem;
  border-radius: var(--radius-sm);
  background: #fff7ed;
  color: #9a3412;
  border: 1px solid #fed7aa;
  line-height: 1.65;
  font-size: .9rem;
}

.layout {
  display: grid;
  grid-template-columns: minmax(320px, 700px) minmax(300px, 1fr);
  gap: 1.25rem;
  align-items: start;
}
.levels-layout {
  grid-template-columns: minmax(300px, .92fr) minmax(320px, 1.08fr);
}
.board-wrap { display: grid; gap: .85rem; position: relative; }
.board-wrap .pass-stamp-overlay {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%) rotate(-14deg);
  z-index: 10;
  pointer-events: none;
}
.pass-stamp {
  display: inline-block;
  font-size: clamp(2.6rem, 7vw, 5rem);
  font-weight: 950;
  color: #16a34a;
  border: clamp(4px, 1vw, 7px) solid #16a34a;
  border-radius: 999px;
  padding: clamp(.58rem, 2vw, 1.15rem) clamp(.95rem, 3vw, 1.85rem);
  letter-spacing: .08em;
  text-transform: uppercase;
  box-shadow: 0 12px 36px rgba(22,163,74,.30);
  background: rgba(255,255,255,.76);
  backdrop-filter: blur(6px);
  line-height: 1;
  user-select: none;
}
.toolbar {
  display: flex;
  flex-wrap: wrap;
  gap: .62rem;
  align-items: center;
  justify-content: space-between;
}
.toolbar-left, .toolbar-right { display: flex; flex-wrap: wrap; gap: .5rem; align-items: center; }
.status-pill {
  display: inline-flex;
  align-items: center;
  gap: .35rem;
  border-radius: 999px;
  padding: .54rem .82rem;
  background: rgba(255,255,255,.82);
  border: 1px solid var(--line);
  color: #374151;
  font-weight: 850;
  font-size: .88rem;
  box-shadow: var(--shadow-sm);
}
.status-pill.check { color: #c2410c; background: #fff7ed; border-color: #fed7aa; }
.status-pill.done { color: var(--ok); background: #f0fdf4; border-color: #bbf7d0; }
.status-pill.error { color: var(--danger); background: #fef2f2; border-color: #fecaca; }

.chessboard {
  width: min(100%, 700px);
  aspect-ratio: 1;
  display: grid;
  grid-template-columns: repeat(8, 1fr);
  grid-template-rows: repeat(8, 1fr);
  overflow: hidden;
  border-radius: 20px;
  border: 10px solid #40362d;
  background: #40362d;
  box-shadow: var(--shadow-lg);
  touch-action: manipulation;
  user-select: none;
}
.square {
  position: relative;
  display: grid;
  place-items: center;
  min-width: 0;
  min-height: 0;
  cursor: pointer;
  transition: box-shadow .12s ease, filter .12s ease;
}
.square.light { background: var(--light-square); }
.square.dark { background: var(--dark-square); }
.square:hover { filter: brightness(1.03); }
.square.selected { outline: 4px solid var(--select); outline-offset: -4px; z-index: 2; }
.square.legal::after {
  content: "";
  width: 26%; height: 26%;
  border-radius: 50%;
  background: var(--legal);
  box-shadow: inset 0 0 0 2px rgba(255,255,255,.30);
}
.square.capture::after {
  content: "";
  position: absolute;
  inset: 7%;
  border: 4px solid var(--capture);
  border-radius: 50%;
}
.square.last-from, .square.last-to { box-shadow: inset 0 0 0 999px rgba(245,158,11,.22); }
.piece {
  position: relative;
  z-index: 1;
  font-size: clamp(2rem, 7.5vw, 4.55rem);
  line-height: 1;
  filter: drop-shadow(0 3px 4px rgba(0,0,0,.20));
  transition: transform .1s ease;
}
.piece.black { color: #15120f; text-shadow: 0 1px 0 rgba(255,255,255,.18); }
.piece.white { color: #fffdf8; text-shadow: 0 2px 5px rgba(0,0,0,.58); }
.piece.invert { transform: rotate(180deg); }
.coord {
  position: absolute;
  z-index: 2;
  font-size: clamp(.52rem, 1.2vw, .72rem);
  font-weight: 900;
  opacity: .68;
  pointer-events: none;
}
.coord.file { bottom: .14rem; right: .22rem; }
.coord.rank { top: .14rem; left: .22rem; }
.square.light .coord { color: #6b5d4f; }
.square.dark .coord { color: #efe7dc; }

.side-panel { padding: 1.12rem; display: grid; gap: .85rem; }
.panel h2, .panel h3, .card h2, .card h3 { margin: 0; font-weight: 900; letter-spacing: -.015em; }
.panel-title { display: flex; align-items: center; justify-content: space-between; gap: .7rem; flex-wrap: wrap; }
.move-log {
  overflow: auto;
  max-height: 420px;
  border-radius: var(--radius-sm);
  background: #f8fafc;
  border: 1px solid var(--line);
}
.move-row {
  display: grid;
  grid-template-columns: 3rem 1fr 1fr;
  gap: .5rem;
  padding: .62rem .78rem;
  border-bottom: 1px solid var(--line);
  align-items: center;
}
.move-row:last-child { border-bottom: 0; }
.move-no { color: var(--muted); font-weight: 900; font-size: .88rem; }
.move-san { font-family: var(--font-mono); font-weight: 780; font-size: .9rem; }
.empty-state {
  padding: 1.05rem;
  border-radius: var(--radius-sm);
  background: rgba(248,250,252,.86);
  color: var(--muted);
  line-height: 1.72;
  text-align: center;
  font-size: .9rem;
  border: 1px dashed rgba(148,163,184,.55);
}
.form-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: .86rem; }
.form-grid .full { grid-column: 1 / -1; }
.switch-line { display: flex; flex-wrap: wrap; align-items: center; gap: .52rem .8rem; }
.switch-line label { display: inline-flex; align-items: center; gap: .35rem; font-weight: 750; font-size: .9rem; }
.switch-line input { width: auto; }

.palette { display: grid; grid-template-columns: repeat(7, 1fr); gap: .4rem; }
.palette button {
  border-radius: 14px;
  padding: .52rem .18rem;
  font-size: 1.35rem;
  color: var(--text);
  background: #f8fafc;
  border: 1px solid var(--line-strong);
  box-shadow: none;
}
.palette button:hover { background: #eef2ff; }
.palette button.active { outline: 3px solid var(--accent); outline-offset: 2px; background: #eff6ff; }
.level-list { display: grid; gap: .82rem; }
.level-item {
  display: grid;
  gap: .68rem;
  padding: 1rem;
  border-radius: var(--radius-sm);
  background: linear-gradient(180deg, rgba(255,255,255,.94), rgba(248,250,252,.88));
  border: 1px solid var(--line);
  transition: transform .14s ease, box-shadow .14s ease, border-color .14s ease;
}
.level-item:hover { transform: translateY(-1px); box-shadow: var(--shadow-sm); border-color: #bfdbfe; }
.level-item.official-item { border-color: #fed7aa; background: linear-gradient(180deg, #fff, #fff7ed); }
.level-item header { display: flex; gap: .72rem; align-items: flex-start; justify-content: space-between; }
.level-title { font-size: 1.02rem; font-weight: 900; }
.level-meta { color: var(--muted); font-size: .85rem; line-height: 1.55; }
.level-desc { color: #4b5563; font-size: .9rem; line-height: 1.62; margin-top: .28rem; }
.level-actions { display: flex; flex-wrap: wrap; gap: .42rem; }
.level-actions button { padding: .52rem .74rem; font-size: .84rem; }
.passed-mark {
  display: inline-flex;
  align-items: center;
  gap: .25rem;
  color: #15803d;
  font-weight: 900;
  font-size: .82rem;
  background: #f0fdf4;
  border-radius: 999px;
  padding: .22rem .6rem;
  border: 1px solid #bbf7d0;
}
.copyright-note {
  padding: .9rem 1rem;
  border-radius: var(--radius-sm);
  color: #9a3412;
  background: #fff7ed;
  border: 1px solid #fed7aa;
  font-size: .9rem;
  line-height: 1.62;
}
.upload-label {
  display: inline-flex;
  align-items: center;
  gap: .5rem;
  border-radius: 999px;
  padding: .72rem 1rem;
  cursor: pointer;
  background: #f8fafc;
  border: 1px solid var(--line);
  color: #1f2937;
  font-weight: 750;
  font-size: .92rem;
  transition: transform .16s ease, box-shadow .18s ease, border-color .18s ease;
}
.upload-label:hover { transform: translateY(-1px); box-shadow: var(--shadow-sm); border-color: #bfdbfe; }
.upload-label input { display: none; }
.solution-box {
  display: grid;
  gap: .35rem;
  max-height: 240px;
  overflow: auto;
  border-radius: var(--radius-sm);
  background: #f8fafc;
  padding: .75rem;
  border: 1px solid var(--line);
}
.solution-line { font-family: var(--font-mono); font-size: .9rem; }
.solution-viewer-layout { display: grid; gap: 1rem; }
.solution-viewer-board { width: min(100%, 380px); margin: 0 auto; }
.solution-viewer-controls {
  display: flex;
  flex-wrap: wrap;
  gap: .45rem;
  justify-content: center;
  align-items: center;
}
.solution-viewer-controls .step-indicator {
  font-weight: 800;
  font-size: .92rem;
  color: var(--text);
  min-width: 6rem;
  text-align: center;
}
.solution-viewer-controls .step-san {
  font-family: var(--font-mono);
  font-weight: 850;
  font-size: 1rem;
  color: var(--accent);
  text-align: center;
  width: 100%;
}
.solution-viewer-controls button { padding: .48rem .72rem; font-size: .84rem; border-radius: 999px; }

.modal {
  position: fixed;
  inset: 0;
  z-index: 100;
  display: grid;
  place-items: center;
  padding: 1rem;
  background: rgba(15,23,42,.48);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
}
.modal.hidden, .toast.hidden { display: none; }
.modal-card {
  width: min(620px, 100%);
  max-height: 92vh;
  overflow-y: auto;
  border-radius: var(--radius);
  background: var(--panel-solid);
  box-shadow: 0 28px 90px rgba(15,23,42,.32);
  padding: 1.2rem;
  display: grid;
  gap: .92rem;
}
.modal-actions { display: flex; flex-wrap: wrap; gap: .55rem; justify-content: flex-end; }
.promo-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: .55rem; }
.promo-grid button { font-size: 1.9rem; border-radius: 16px; padding: .9rem .35rem; }
.toast {
  position: fixed;
  z-index: 120;
  left: 50%;
  bottom: 1.35rem;
  transform: translateX(-50%);
  max-width: min(600px, calc(100% - 2rem));
  border-radius: 999px;
  background: rgba(17,24,39,.94);
  color: #fff;
  padding: .82rem 1.15rem;
  box-shadow: 0 16px 46px rgba(15,23,42,.26);
  text-align: center;
  font-weight: 760;
  font-size: .9rem;
}
.site-footer {
  display: flex;
  flex-wrap: wrap;
  gap: .55rem 1rem;
  justify-content: center;
  padding: 1.4rem 1rem 2.35rem;
  color: var(--muted);
  border-top: 1px solid rgba(203,213,225,.75);
  font-size: .84rem;
  text-align: center;
}

@media (max-width: 980px) {
  .site-header { align-items: flex-start; flex-direction: column; }
  .top-nav { justify-content: flex-start; }
  .hero, .layout, .levels-layout { grid-template-columns: 1fr; }
  .hero-card { min-height: auto; }
  .chessboard { margin-inline: auto; border-width: 7px; border-radius: 18px; }
  .move-log { max-height: 260px; }
  .solution-viewer-board { width: min(100%, 300px); }
}
@media (max-width: 620px) {
  .app-shell { width: min(100% - .7rem, 1280px); margin-top: .7rem; }
  .site-header { padding: .72rem; }
  .brand p { display: none; }
  .top-nav { width: 100%; display: grid; grid-template-columns: repeat(2, 1fr); }
  .top-nav button { width: 100%; }
  .card, .side-panel { padding: .85rem; }
  .action-grid, .form-grid, .stat-grid { grid-template-columns: 1fr; }
  .chessboard { border-width: 5px; border-radius: 14px; }
  .move-row { grid-template-columns: 2.4rem 1fr 1fr; font-size: .85rem; padding: .52rem .55rem; }
  .palette { grid-template-columns: repeat(4, 1fr); }
  .toolbar { align-items: stretch; }
  .toolbar-left, .toolbar-right { width: 100%; }
  .toolbar button, .toolbar select, .upload-label { flex: 1 1 auto; justify-content: center; font-size: .84rem; padding: .55rem .66rem; }
  .pass-stamp { font-size: 2.2rem; padding: .5rem .74rem; border-width: 4px; }
  .solution-viewer-board { width: min(100%, 260px); }
  .solution-viewer-controls button { padding: .42rem .58rem; font-size: .78rem; }
}