/* Thème sombre, sobre & futuriste */
:root{
  --bg:#0b0f14;
  --card:#111720;
  --edge:#1d2531;
  --ink:#e6edf3;
  --muted:#9fb0c0;
  --accent:#4dd0e1;
  --accent-2:#8a63d2;
  --hot:#f05454;
  --good:#62d36b;
  --warn:#f0c454;
}

*{box-sizing:border-box}
html,body{height:100%}
body{
  margin:0;
  font-family: ui-sans-serif, system-ui, -apple-system, Segoe UI, Roboto, "Helvetica Neue", Arial, "Noto Sans", "Liberation Sans", sans-serif;
  background: radial-gradient(1200px 600px at 20% -10%, #0f1621 0%, var(--bg) 55%);
  color:var(--ink);
}

.app{
  max-width:1100px;
  margin:0 auto;
  padding:16px;
}

header{
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:16px;
  margin-bottom:12px;
}

h1{
  margin:0;
  font-weight:700;
  letter-spacing:0.3px;
  background: linear-gradient(90deg,var(--accent),var(--accent-2));
  -webkit-background-clip:text;
  background-clip:text;
  color:transparent;
}

.meta{
  display:flex;
  gap:16px;
  font-size:14px;
  color:var(--muted);
}
.meta .meta-item span{ color:var(--ink); font-weight:600;}

main{
  display:grid;
  grid-template-columns: 1fr 320px;
  gap:16px;
}
@media (max-width: 900px){
  main{ grid-template-columns: 1fr; }
}

.board-wrapper{
  background: linear-gradient(180deg,rgba(77,208,225,0.04), transparent 30%);
  padding:12px;
  border-radius:12px;
  border:1px solid var(--edge);
}

.board{
  aspect-ratio:1/1;
  width:100%;
  max-width:720px;
  margin:auto;
  display:grid;
  grid-template-columns: repeat(9, 1fr);
  grid-template-rows: repeat(9, 1fr);
  gap:2px;
  background:var(--edge);
  border:2px solid var(--edge);
  border-radius:10px;
  box-shadow: 0 0 0 1px rgba(77,208,225,0.15), 0 20px 50px rgba(0,0,0,0.35);
}

.cell{
  background:var(--card);
  display:grid;
  place-items:center;
  position:relative;
  cursor:pointer;
  user-select:none;
  font-variant-numeric: tabular-nums;
  transition: background 120ms ease;
}
.cell.locked{ color:var(--muted); cursor:default; }
.cell.selected{ outline:2px solid var(--accent); z-index:2; }
.cell.highlight{ background: #18202b; }

.cell .value{
  font-size: clamp(16px, 2.2vw, 28px);
  font-weight:700;
}
.cell .pencil{
  position:absolute; inset:2px;
  display:grid; grid-template-columns:repeat(3,1fr); grid-template-rows:repeat(3,1fr);
  gap:1px; opacity:0.9; font-size:10px;
}
.pencil div{ display:grid; place-items:center; color:var(--muted); }

/* blocs 3x3 */
.cell.b-right{ border-right:2px solid var(--edge); }
.cell.b-bottom{ border-bottom:2px solid var(--edge); }

.panel{
  position:relative;
  background:linear-gradient(180deg, rgba(138,99,210,0.07), transparent 40%);
  border:1px solid var(--edge);
  border-radius:12px;
  padding:12px;
}
.numpad{
  display:grid;
  grid-template-columns: repeat(5,1fr);
  gap:8px;
}
.numpad .num{
  padding:10px 0;
  font-weight:700;
  border:1px solid var(--edge);
  background:var(--card);
  color:var(--ink);
  border-radius:8px;
  cursor:pointer;
}
.numpad .num:active{ transform:translateY(1px); }

.controls, .persist{
  display:grid;
  grid-template-columns: repeat(3,1fr);
  gap:8px;
  margin-top:10px;
}
.controls button, .persist button, .import{
  padding:10px 8px;
  border:1px solid var(--edge);
  background:linear-gradient(180deg,#131b25,#101621);
  color:var(--ink);
  border-radius:8px;
  cursor:pointer;
  font-size:14px;
  text-align:center;
}
.import input{ display:none; }

.difficulty{ margin-top:10px; display:flex; align-items:center; gap:8px; }
.difficulty select{
  flex:1;
  padding:8px;
  border-radius:8px;
  background:var(--card);
  border:1px solid var(--edge);
  color:var(--ink);
}

.progress{ margin-top:12px; height:8px; background:#141a24; border:1px solid var(--edge); border-radius:999px; overflow:hidden; }
#progress-bar{ height:100%; width:0%; background:linear-gradient(90deg,var(--accent),var(--accent-2)); }

.help{
  margin-top:12px;
  color:var(--muted);
}
.help summary{ cursor:pointer; color:var(--ink); }

footer{ margin-top:16px; color:var(--muted); text-align:center; }