:root {
  --bg: #0e1320;
  --panel: #161d2e;
  --panel-2: #1d2740;
  --line: #29334d;
  --text: #e7ecf6;
  --muted: #95a1bd;
  --brand: #4f8cff;
  --brand-2: #2f6ae0;
  --ok: #2fbf71;
  --warn: #ffb020;
  --flag: #12d18e;
  --danger: #ff5d5d;
}
* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: "Segoe UI", Roboto, system-ui, sans-serif;
  background: radial-gradient(1200px 600px at 20% -10%, #1a2340 0, transparent 60%), var(--bg);
  color: var(--text);
  min-height: 100vh;
}
a { color: var(--brand); text-decoration: none; }
a:hover { text-decoration: underline; }

.topbar {
  background: #101728;
  border-bottom: 1px solid var(--line);
  padding: 12px 22px;
  display: flex;
  align-items: center;
  gap: 18px;
  position: sticky; top: 0; z-index: 20;
}
.logo { font-weight: 700; letter-spacing: .3px; font-size: 18px; display: flex; align-items: center; gap: 10px; }
.logo .dot { width: 10px; height: 10px; border-radius: 50%; background: var(--brand); box-shadow: 0 0 12px var(--brand); }
.logo small { color: var(--muted); font-weight: 400; }
.nav { display: flex; gap: 4px; flex-wrap: wrap; margin-left: 8px; }
.nav a {
  padding: 7px 12px; border-radius: 8px; color: var(--muted);
  font-size: 14px;
}
.nav a:hover { background: var(--panel-2); color: var(--text); text-decoration: none; }
.who { margin-left: auto; font-size: 13px; color: var(--muted); display: flex; gap: 12px; align-items: center; }

.lab-band {
  background: linear-gradient(90deg, #3a2a00, #4a3600);
  color: #ffe4a1;
  font-size: 13px;
  padding: 8px 22px;
  border-bottom: 1px solid #6b4e00;
}

.wrap { max-width: 1020px; margin: 0 auto; padding: 26px 20px 60px; }
h1 { font-size: 24px; margin: 0 0 6px; }
h2 { font-size: 18px; margin: 28px 0 10px; }
p.lead { color: var(--muted); margin-top: 0; }

.card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 18px 20px;
  margin: 16px 0;
}
.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: 14px; }
.chal { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 16px; display: flex; flex-direction: column; gap: 8px; }
.chal h3 { margin: 0; font-size: 15px; display: flex; align-items: center; gap: 8px; }
.badge { font-size: 11px; padding: 2px 8px; border-radius: 999px; border: 1px solid var(--line); color: var(--muted); }
.badge.solved { color: #06210f; background: var(--ok); border-color: var(--ok); font-weight: 700; }
.chal p { color: var(--muted); font-size: 13px; margin: 0; flex: 1; }
.chal .go { font-size: 13px; }

.btn {
  display: inline-block; background: var(--brand-2); color: #fff; border: 0;
  padding: 9px 14px; border-radius: 8px; font-size: 14px; cursor: pointer;
}
.btn:hover { background: var(--brand); text-decoration: none; color: #fff; }
.btn.ghost { background: transparent; border: 1px solid var(--line); color: var(--text); }

input, textarea, select {
  width: 100%; padding: 10px 12px; border-radius: 8px; border: 1px solid var(--line);
  background: #0f1524; color: var(--text); font-size: 14px; font-family: inherit;
}
label { display: block; font-size: 13px; color: var(--muted); margin: 12px 0 5px; }
.row { display: flex; gap: 10px; }

table { width: 100%; border-collapse: collapse; font-size: 14px; margin-top: 12px; }
th, td { text-align: left; padding: 9px 10px; border-bottom: 1px solid var(--line); }
th { color: var(--muted); font-weight: 600; font-size: 12px; text-transform: uppercase; letter-spacing: .5px; }
tr:hover td { background: #1a2237; }

pre {
  background: #0b1120; border: 1px solid var(--line); border-radius: 8px;
  padding: 12px; overflow-x: auto; font-size: 13px; color: #c7d3ee;
}
code { background: #0b1120; padding: 2px 6px; border-radius: 6px; font-size: 13px; }

.flag {
  background: rgba(18, 209, 142, .12);
  border: 1px solid var(--flag);
  color: #b9ffe4;
  border-radius: 10px;
  padding: 14px 16px;
  margin: 14px 0;
  font-size: 14px;
}
.flag strong { color: var(--flag); }
.flag code { background: rgba(18,209,142,.18); color: #d8fff0; font-weight: 700; }

.error { background: rgba(255,93,93,.12); border: 1px solid var(--danger); color: #ffc9c9; border-radius: 10px; padding: 12px 14px; margin: 12px 0; font-size: 14px; }
.notice { background: rgba(79,140,255,.12); border: 1px solid #2f6ae0; color: #cfe0ff; border-radius: 10px; padding: 12px 14px; margin: 12px 0; font-size: 14px; }
.muted { color: var(--muted); }
.small { font-size: 13px; }
.hint { font-size: 13px; color: var(--warn); }
footer { color: var(--muted); font-size: 12px; text-align: center; padding: 30px; border-top: 1px solid var(--line); margin-top: 40px; }

/* ── Difficulty tiers, hint toggles, live scoreboard ─────────────────────── */
.badge.level { text-transform: capitalize; }
.badge.level.beginner { border-color: var(--ok); color: #7ee787; }
.badge.level.intermediate { border-color: var(--warn); color: #e3b341; }
.badge.level.advanced { border-color: var(--danger); color: #ff9d9d; }

details.hints { font-size: 13px; }
details.hints summary { cursor: pointer; color: var(--warn); list-style: none; }
details.hints summary::-webkit-details-marker { display: none; }
details.hints summary::before { content: '▸ '; }
details.hints[open] summary::before { content: '▾ '; }
details.hints p { margin: 8px 0 0; color: var(--muted); }

.tiers { display: flex; flex-wrap: wrap; gap: 8px; margin: 12px 0 18px; }
.chip { background: var(--panel); color: var(--text); border: 1px solid var(--line); border-radius: 999px; padding: 7px 14px; cursor: pointer; font-size: 13px; }
.chip:hover { border-color: var(--brand); }
.chip.active { background: var(--brand-2); border-color: var(--brand); color: #fff; font-weight: 700; }

.live { display: inline-flex; align-items: center; gap: 6px; font-size: 12px; color: var(--muted); }
.live .dot { width: 8px; height: 8px; border-radius: 50%; background: var(--ok); animation: pulse 2s infinite; }
@keyframes pulse {
  0% { box-shadow: 0 0 0 0 rgba(47, 191, 113, .6); }
  70% { box-shadow: 0 0 0 7px rgba(47, 191, 113, 0); }
  100% { box-shadow: 0 0 0 0 rgba(47, 191, 113, 0); }
}
.meter { height: 10px; background: #0f1524; border: 1px solid var(--line); border-radius: 999px; overflow: hidden; margin: 10px 0; }
.meter span { display: block; height: 100%; background: var(--ok); transition: width .3s ease; }
.meter.small { height: 7px; margin: 0; min-width: 90px; }

/* Scroll container so wide tables never break the layout on small screens */
.table-wrap { width: 100%; overflow-x: auto; -webkit-overflow-scrolling: touch; border-radius: 8px; }
.table-wrap table { min-width: 460px; }

/* Make sure long content can never force a horizontal page scroll */
img, pre, code { max-width: 100%; }
pre { white-space: pre-wrap; word-break: break-word; }

/* ══ Mobile / responsive ══════════════════════════════════════════════════ */
@media (max-width: 820px) {
  .topbar { flex-wrap: wrap; gap: 10px 12px; padding: 10px 14px; }
  .logo { font-size: 16px; }
  .logo small { display: none; }
  .nav {
    order: 3;
    width: 100%;
    margin-left: 0;
    flex-wrap: nowrap;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
    padding-bottom: 3px;
  }
  .nav a { flex: 0 0 auto; padding: 6px 11px; font-size: 13px; }
  .who { margin-left: auto; font-size: 12px; gap: 8px; }
  .lab-band { padding: 8px 14px; font-size: 12px; line-height: 1.5; }
  .wrap { padding: 18px 14px 48px; }
  h1 { font-size: 21px; }
  h2 { font-size: 17px; margin: 22px 0 8px; }
}

@media (max-width: 600px) {
  .grid { grid-template-columns: 1fr; gap: 12px; }
  .card { padding: 15px; margin: 13px 0; }
  .chal { padding: 14px; }
  .row { flex-direction: column; gap: 8px; }
  .row > * { width: 100%; }
  .btn { display: block; width: 100%; text-align: center; padding: 11px 14px; }
  .btn.ghost { display: inline-block; width: auto; padding: 7px 12px; }
  th, td { padding: 8px 9px; font-size: 13px; }
  pre { font-size: 12px; padding: 11px; }
  /* 16px keeps iOS Safari from zooming when a field is focused */
  input, textarea, select { font-size: 16px; }
  footer { padding: 22px 16px; }
}

@media (max-width: 400px) {
  .wrap { padding: 14px 11px 40px; }
  h1 { font-size: 19px; }
  .who span { display: none; }
}