/* ===== Excel Arena — design system ===== */
:root {
  --bg: #0b0e1a;
  --bg-2: #111629;
  --surface: #141a2e;
  --surface-2: #1c2340;
  --border: #28304f;
  --text: #e9ecf9;
  --muted: #97a0c2;
  --accent: #4053ef;
  --accent-2: #6b7bff;
  --accent-soft: rgba(64, 83, 239, 0.16);
  --accent-ink: #ffffff;
  --easy: #3fd07a;
  --medium: #f2c14e;
  --hard: #f2685c;
  --shade-1: rgba(11, 14, 26, 0.15);
  --shade-2: rgba(11, 14, 26, 0.85);
  --shade-3: rgba(11, 14, 26, 0.97);
  --hud-bg: rgba(11, 14, 26, 0.92);
  --card-img-opacity: 0.5;
  --radius: 14px;
  --shadow: 0 18px 40px -22px rgba(0, 0, 0, 0.9);
  --mono: "IBM Plex Mono", ui-monospace, SFMono-Regular, Menlo, monospace;
  --sans: "Space Grotesk", system-ui, -apple-system, sans-serif;
}

html[data-theme="light"] {
  --bg: #f5f6fc;
  --bg-2: #eceffa;
  --surface: #ffffff;
  --surface-2: #f0f2fb;
  --border: #dfe3f2;
  --text: #121628;
  --muted: #5f688a;
  --accent: #4053ef;
  --accent-2: #2b3ad6;
  --accent-soft: rgba(64, 83, 239, 0.12);
  --accent-ink: #ffffff;
  --easy: #17a35a;
  --medium: #b7830f;
  --hard: #d63b2c;
  --shade-1: rgba(255, 255, 255, 0.1);
  --shade-2: rgba(10, 14, 30, 0.6);
  --shade-3: rgba(10, 14, 30, 0.9);
  --hud-bg: rgba(245, 246, 252, 0.92);
  --card-img-opacity: 0.85;
  --shadow: 0 18px 40px -26px rgba(20, 26, 60, 0.45);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 150px; }

body {
  margin: 0;
  background:
    radial-gradient(1100px 600px at 80% -10%, var(--accent-soft), transparent 60%),
    var(--bg);
  color: var(--text);
  font-family: var(--sans);
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
  transition: background-color 0.2s ease, color 0.2s ease;
}

a { color: inherit; }

.wrap { width: min(1080px, 92vw); margin: 0 auto; }

/* ---- top nav ---- */
.nav {
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 22px 0;
}
.brand {
  display: flex; align-items: center; gap: 10px;
  font-weight: 700; letter-spacing: -0.02em; text-decoration: none;
  margin-right: auto;
}
.brand .logo { width: 32px; height: 32px; border-radius: 0px; object-fit: contain; flex: none; }
.lang-toggle {
  display: inline-flex; align-items: center; gap: 4px;
  height: 38px; padding: 0 5px; flex: none;
  border-radius: 10px; cursor: pointer;
  border: 1px solid var(--border); background: var(--surface-2); color: var(--text);
  font: inherit;
}
.lang-toggle:hover { border-color: var(--accent); }
.lang-toggle .flag {
  width: 26px; height: 17px; border-radius: 3px; overflow: hidden;
  opacity: 0.4; filter: grayscale(1);
  box-shadow: 0 0 0 1px var(--border);
  object-fit: cover;
  transition: opacity 0.18s ease, filter 0.18s ease, box-shadow 0.18s ease, transform 0.18s ease;
}
.lang-toggle .flag.on { opacity: 1; filter: none; box-shadow: 0 0 0 0px var(--accent); transform: scale(1.05); }
.brand .mark {
  width: 26px; height: 26px; border-radius: 7px;
  background: linear-gradient(140deg, var(--accent-2), var(--accent));
  box-shadow: 0 0 0 1px rgba(255, 255, 255, 0.08) inset;
}
.nav a.link { color: var(--muted); text-decoration: none; font-size: 0.95rem; }
.nav a.link:hover { color: var(--text); }

/* ---- theme toggle ---- */
.theme-toggle {
  display: inline-flex; align-items: center; justify-content: center;
  width: 38px; height: 38px; flex: none;
  border-radius: 10px; cursor: pointer;
  border: 1px solid var(--border);
  background: var(--surface-2);
  color: var(--text);
  font-size: 1rem;
  line-height: 1;
  transition: border-color 0.15s ease, background 0.15s ease;
}
.theme-toggle:hover { border-color: var(--accent); color: var(--accent); }

/* ---- buttons ---- */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  border: 1px solid var(--border);
  background: var(--surface-2);
  color: var(--text);
  padding: 11px 18px;
  border-radius: 10px;
  font: inherit;
  font-weight: 600;
  cursor: pointer;
  text-decoration: none;
  transition: transform 0.12s ease, background 0.15s ease, border-color 0.15s ease;
}
.btn:hover { transform: translateY(-1px); border-color: var(--accent); }
.btn:active { transform: translateY(0); }
.btn-primary {
  background: linear-gradient(140deg, var(--accent-2), var(--accent));
  color: var(--accent-ink);
  border-color: transparent;
}
.btn-ghost { background: transparent; }
.btn-danger { color: var(--hard); border-color: rgba(242, 104, 92, 0.35); background: rgba(242, 104, 92, 0.08); }
.btn-sm { padding: 7px 12px; font-size: 0.85rem; }
.btn[disabled] { opacity: 0.45; cursor: not-allowed; transform: none; }

/* ---- home ---- */
.hero { padding: 12vh 0 10vh; max-width: 640px; }
.eyebrow {
  font-family: var(--mono); font-size: 0.75rem; letter-spacing: 0.22em;
  text-transform: uppercase; color: var(--accent);
}
h1 { font-size: clamp(2.4rem, 6vw, 3.8rem); line-height: 1.05; letter-spacing: -0.035em; margin: 14px 0 0; }
.lede { color: var(--muted); font-size: 1.08rem; margin: 18px 0 32px; }

/* ---- challenge grid ---- */
.page-head { padding: 26px 0 30px; }
.page-head h1 { font-size: clamp(1.9rem, 4vw, 2.6rem); }
.page-head p { color: var(--muted); margin: 8px 0 0; }

.grid {
  display: grid; gap: 20px;
  grid-template-columns: repeat(auto-fill, minmax(290px, 1fr));
  padding-bottom: 80px;
}
.card {
  position: relative; display: flex; flex-direction: column; overflow: hidden;
  border-radius: var(--radius); border: 1px solid var(--border);
  background: var(--surface);
  box-shadow: var(--shadow);
  transition: transform 0.16s ease, border-color 0.16s ease;
}
.card:hover { transform: translateY(-3px); border-color: var(--accent); }
.card-media { position: relative; display: block; aspect-ratio: 16 / 9; overflow: hidden; }
.card-media img { width: 100%; height: 100%; object-fit: cover; display: block; }
.card-tags { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; }
.card-enter { animation: card-in 0.32s cubic-bezier(0.22, 0.8, 0.3, 1) both; }
@keyframes card-in {
  from { opacity: 0; transform: translateY(10px) scale(0.98); }
  to { opacity: 1; transform: none; }
}
@media (prefers-reduced-motion: reduce) { .card-enter { animation: none; } }
.card-info { display: flex; flex-direction: column; gap: 12px; padding: 16px 18px 18px; }
.card-info h2 { margin: 0; font-size: 1.2rem; letter-spacing: -0.02em; }
.cat-tag {
  align-self: flex-start; font-family: var(--mono); font-size: 0.68rem;
  letter-spacing: 0.14em; text-transform: uppercase; color: var(--accent);
  background: var(--accent-soft); border-radius: 999px; padding: 3px 10px;
}
.card-facts { display: grid; grid-template-columns: repeat(4, 1fr); gap: 8px; margin: 0; }
.card-facts div { display: flex; flex-direction: column; gap: 2px; }
.card-facts dt { font-size: 0.64rem; letter-spacing: 0.1em; text-transform: uppercase; color: var(--muted); }
.card-facts dd { margin: 0; font-family: var(--mono); font-size: 0.95rem; }
.card-open { align-self: flex-start; }

/* ---- filters ---- */
.filters { display: flex; flex-wrap: wrap; align-items: center; gap: 14px 22px; margin-bottom: 26px; }
.search {
  flex: 1 1 240px; min-width: 200px;
  background: var(--surface); border: 1px solid var(--border); border-radius: 10px;
  color: var(--text); font: inherit; padding: 10px 14px; outline: none;
}
.search:focus { border-color: var(--accent); }
.filter-group { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.filter-label { font-size: 0.72rem; letter-spacing: 0.14em; text-transform: uppercase; color: var(--muted); }
.empty { color: var(--muted); }

.chip {
  display: inline-flex; align-items: center; gap: 6px;
  align-self: flex-start;
  padding: 4px 11px; border-radius: 999px;
  font-size: 0.74rem; font-weight: 700; letter-spacing: 0.08em; text-transform: uppercase;
}
.chip::before { content: ""; width: 7px; height: 7px; border-radius: 50%; background: currentColor; }
.chip-easy { color: var(--easy); background: rgba(63, 208, 122, 0.14); }
.chip-medium { color: var(--medium); background: rgba(242, 193, 78, 0.14); }
.chip-hard { color: var(--hard); background: rgba(242, 104, 92, 0.14); }

/* ---- challenge detail ---- */
.detail {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr);
  grid-template-areas: "media setup" "copy copy";
  gap: 26px 34px; padding: 20px 0 28px; align-items: start;
}
.detail-media { grid-area: media; }
.detail-copy { grid-area: copy; }
.setup-panel { grid-area: setup; }
.detail.started { grid-template-areas: "media copy"; gap: 34px; }
@media (max-width: 820px) {
  .detail, .detail.started { grid-template-columns: 1fr; grid-template-areas: "media" "copy" "setup"; }
  .detail.started { grid-template-areas: "media" "copy"; }
}
.detail-copy h1 { margin-top: 0; }
.detail-tags { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.meta-line { font-family: var(--mono); font-size: 0.85rem; }
.setup-panel { margin-bottom: 0; }

.detail-img { width: 100%; border-radius: var(--radius); border: 1px solid var(--border); display: block; }
.detail h1 { font-size: clamp(1.8rem, 4vw, 2.5rem); margin: 14px 0 10px; }
.detail p.desc { color: var(--muted); }

.panel {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 20px; box-shadow: var(--shadow);
}
.panel h3 { margin: 0 0 14px; font-size: 0.8rem; letter-spacing: 0.16em; text-transform: uppercase; color: var(--muted); }
.opt { margin-bottom: 18px; }
.opt-label { font-size: 0.85rem; color: var(--muted); margin-bottom: 8px; }
.seg { display: flex; gap: 8px; flex-wrap: wrap; }
.seg button {
  border: 1px solid var(--border); background: var(--bg-2); color: var(--muted);
  padding: 8px 14px; border-radius: 9px; font: inherit; font-size: 0.9rem; cursor: pointer;
}
.seg button.on { background: var(--accent-soft); border-color: var(--accent); color: var(--accent); }

.switch { display: flex; align-items: center; gap: 12px; cursor: pointer; -webkit-user-select:none; user-select: none; }
.switch input { display: none; }
.track { width: 44px; height: 25px; border-radius: 999px; background: var(--surface-2); border: 1px solid var(--border); position: relative; transition: 0.18s; flex: none; }
.track::after { content: ""; position: absolute; top: 2px; left: 2px; width: 19px; height: 19px; border-radius: 50%; background: var(--muted); transition: 0.18s; }
.switch input:checked + .track { background: var(--accent-soft); border-color: var(--accent); }
.switch input:checked + .track::after { transform: translateX(19px); background: var(--accent); }

.best { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-top: 18px; padding-top: 16px; border-top: 1px solid var(--border); }
.best-val { font-family: var(--mono); font-size: 1.35rem; color: var(--accent); }
.best-lbl { font-size: 0.78rem; color: var(--muted); letter-spacing: 0.1em; text-transform: uppercase; }

/* ---- sticky HUD ---- */
.hud {
  position: sticky; top: 0; z-index: 40;
  background: var(--hud-bg);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
  margin-bottom: 26px;
}
.hud-inner { display: flex; align-items: center; gap: 16px; flex-wrap: wrap; padding: 12px 0; }
.stat { display: flex; flex-direction: column; line-height: 1.15; }
.stat span { font-size: 0.68rem; letter-spacing: 0.16em; text-transform: uppercase; color: var(--muted); }
.stat strong { font-family: var(--mono); font-size: 1.5rem; font-weight: 600; }
#hudTimer.low { color: var(--hard); }
.hud-jumps { display: flex; gap: 10px; flex-wrap: wrap; margin-left: auto; }
.hud .switch { font-size: 0.88rem; }

/* ---- level jump buttons with progress ring ---- */
.jump {
  position: relative;
  display: inline-flex; align-items: center; gap: 7px;
  padding: 8px 13px; border-radius: 11px;
  border: 1px solid var(--border); background: var(--surface);
  color: var(--text); font: inherit; font-size: 0.85rem; font-weight: 600;
  text-decoration: none; cursor: pointer;
}
.jump:hover { border-color: var(--accent); }
.jump::after {
  content: "";
  position: absolute; inset: -3px;
  border-radius: 13px;
  padding: 3px;
  background: conic-gradient(
    var(--ring, var(--hard)) 0 var(--filled, 0%),
    transparent var(--filled, 0%) 100%
  );
  -webkit-mask: linear-gradient(#000 0 0) content-box, linear-gradient(#000 0 0);
  -webkit-mask-composite: xor;
  mask: linear-gradient(#000 0 0) content-box, linear-gradient(#000 0 0);
  mask-composite: exclude;
  pointer-events: none;
  transition: background 0.25s ease;
}
.jump .dot { width: 8px; height: 8px; border-radius: 50%; background: var(--border); flex: none; }
.jump.solved { --ring: var(--easy); --filled: 100%; }
.jump.solved .dot { background: var(--easy); }
.jump.partial .dot { background: var(--hard); }
.jump .frac { font-family: var(--mono); font-size: 0.72rem; color: var(--muted); }

/* ---- questions ---- */
.level { margin-bottom: 34px; }
.level-head { display: flex; align-items: baseline; gap: 12px; flex-wrap: wrap; margin-bottom: 12px; }
.level-head h2 { margin: 0; font-size: 1.15rem; letter-spacing: -0.01em; }
.level-head .pts { font-family: var(--mono); font-size: 0.8rem; color: var(--muted); }
.level-head .lvl-score {
  font-family: var(--mono); font-size: 0.82rem; font-weight: 600;
  padding: 3px 10px; border-radius: 999px;
  background: var(--surface-2); border: 1px solid var(--border); color: var(--muted);
  margin-left: auto;
}
.level-head .lvl-score.full { color: var(--easy); border-color: var(--easy); background: rgba(63, 208, 122, 0.12); }
.level-head .lvl-score.some { color: var(--accent); border-color: var(--accent); background: var(--accent-soft); }

.qgrid { display: flex; flex-direction: column; gap: 8px; }
.q { display: flex; align-items: center; gap: 12px; background: var(--surface); border: 1px solid var(--border); border-radius: 11px; padding: 8px 14px; transition: box-shadow 0.18s, border-color 0.18s; }
.qnum { font-family: var(--mono); font-size: 0.85rem; color: var(--muted); min-width: 30px; text-align: center; }
.q input {
  flex: 1; min-width: 0; background: transparent; border: 0; outline: none;
  color: var(--text); font: inherit; font-family: var(--mono); font-size: 0.95rem; padding: 6px 0;
}
.q .qpts { font-family: var(--mono); font-size: 0.72rem; color: var(--muted); }
.q.correct { border-color: var(--easy); box-shadow: 0 0 0 3px rgba(63, 208, 122, 0.16); }
.q.wrong { border-color: var(--hard); box-shadow: 0 0 0 3px rgba(242, 104, 92, 0.14); }
.q.bonus .qnum { color: var(--medium); }

.hidden { display: none !important; }

.dl { display: flex; flex-direction: column; align-items: stretch; gap: 12px; background: var(--accent-soft); border: 1px solid var(--accent); border-radius: var(--radius); padding: 16px 18px; margin-top: 20px; }
.dl p { margin: 0; color: var(--muted); font-size: 0.92rem; }
.btn-lg { width: 100%; padding: 16px 22px; font-size: 1.05rem; border-radius: 12px; }

/* ---- results ---- */
.result { text-align: center; padding: 34px; margin-bottom: 30px; }
.result .big { font-family: var(--mono); font-size: 3rem; color: var(--accent); line-height: 1; }
.result .big .plus { color: var(--easy); }
.result .big .eq { color: var(--text); }
.result ul { list-style: none; padding: 0; margin: 18px 0 0; color: var(--muted); font-family: var(--mono); font-size: 0.9rem; }
.result-actions { margin-top: 18px; display: flex; gap: 10px; justify-content: center; flex-wrap: wrap; }
.share-note { margin: 12px 0 0; color: var(--easy); font-size: 0.85rem; }

footer { color: var(--muted); font-size: 0.82rem; padding: 40px 0; border-top: 1px solid var(--border); margin-top: 40px; }

.site-footer {
  display: flex; align-items: center; justify-content: space-between;
  gap: 16px; flex-wrap: wrap;
  color: var(--muted); font-size: 0.85rem;
  padding: 28px 0 50px; border-top: 1px solid var(--border); margin-top: 20px;
}
.site-footer > div { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.site-footer .logo { border-radius: 7px; object-fit: contain; }
.foot-links a { text-decoration: none; }
.foot-links a:hover { color: var(--accent); }