/* ==========================================================================
   AlgoTasks — базовые стили
   ========================================================================== */
:root {
  --bg: #0e1220;
  --bg-soft: #151b2d;
  --card: #1a2138;
  --card-2: #212a45;
  --line: #2b3556;
  --text: #e8ecf7;
  --muted: #98a3c0;
  --accent: #5b8cff;
  --accent-2: #8f6bff;
  --easy: #2ecc71;
  --medium: #f1c40f;
  --hard: #ff5c72;
  --radius: 14px;
  --shadow: 0 8px 24px rgba(0, 0, 0, .28);
  --mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue",
          Arial, "Noto Sans", sans-serif;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.65;
  color: var(--text);
  background:
    radial-gradient(1200px 600px at 80% -10%, rgba(91, 140, 255, .18), transparent 60%),
    radial-gradient(900px 500px at 0% 0%, rgba(143, 107, 255, .14), transparent 55%),
    var(--bg);
  -webkit-font-smoothing: antialiased;
}

.container {
  width: 100%;
  max-width: 1080px;
  margin-inline: auto;
  padding-inline: 20px;
}

a { color: var(--accent); text-decoration: none; }
a:hover, a:focus-visible { text-decoration: underline; }

/* ---------- Header ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  backdrop-filter: blur(10px);
  background: rgba(14, 18, 32, .78);
  border-bottom: 1px solid var(--line);
}

.site-header .container {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 12px 24px;
  min-height: 64px;
}

.logo {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-weight: 700;
  font-size: 18px;
  color: var(--text);
  letter-spacing: .2px;
}
.logo:hover { text-decoration: none; }
.logo-mark {
  display: grid;
  place-items: center;
  width: 32px;
  height: 32px;
  border-radius: 9px;
  font-size: 15px;
  color: #fff;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
}

.site-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 4px;
  margin-left: auto;
}

.site-nav a {
  padding: 7px 12px;
  border-radius: 999px;
  color: var(--muted);
  font-size: 14px;
  font-weight: 500;
}
.site-nav a:hover { color: var(--text); background: var(--card); text-decoration: none; }
.site-nav a[aria-current="page"] {
  color: #fff;
  background: linear-gradient(135deg, rgba(91, 140, 255, .28), rgba(143, 107, 255, .28));
  box-shadow: inset 0 0 0 1px rgba(143, 107, 255, .45);
}

/* ---------- Hero ---------- */
.hero { padding: 56px 0 28px; }
.hero h1 {
  margin: 0 0 12px;
  font-size: clamp(30px, 5vw, 44px);
  line-height: 1.15;
  letter-spacing: -.5px;
}
.hero p { margin: 0; max-width: 68ch; color: var(--muted); font-size: 17px; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 24px; }

.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 18px;
  border-radius: 999px;
  font-weight: 600;
  font-size: 15px;
  color: #fff;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  box-shadow: var(--shadow);
}
.btn:hover { text-decoration: none; filter: brightness(1.08); }
.btn.secondary {
  color: var(--text);
  background: var(--card);
  box-shadow: inset 0 0 0 1px var(--line);
}

/* ---------- Section titles ---------- */
.section { padding: 28px 0 8px; }
.section h2 {
  margin: 0 0 6px;
  font-size: 24px;
  letter-spacing: -.2px;
}
.section > .container > p.lede { margin: 0 0 20px; color: var(--muted); }

/* ---------- Cards grid (home) ---------- */
.grid {
  display: grid;
  gap: 18px;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
}

.card {
  display: block;
  padding: 20px;
  border-radius: var(--radius);
  color: inherit;
  background: linear-gradient(180deg, var(--card-2), var(--card));
  box-shadow: inset 0 0 0 1px var(--line);
  transition: transform .15s ease, box-shadow .15s ease;
}
.card:hover {
  transform: translateY(-3px);
  text-decoration: none;
  box-shadow: inset 0 0 0 1px var(--accent), var(--shadow);
}
.card-icon { font-size: 26px; }
.card h3 { margin: 10px 0 6px; font-size: 18px; }
.card p { margin: 0 0 12px; color: var(--muted); font-size: 14.5px; }
.card-meta {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 13px;
  color: var(--muted);
}

/* ---------- Stats ---------- */
.stats {
  display: grid;
  gap: 14px;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  margin-top: 28px;
}
.stat {
  padding: 16px;
  border-radius: var(--radius);
  background: var(--card);
  box-shadow: inset 0 0 0 1px var(--line);
}
.stat b { display: block; font-size: 26px; }
.stat span { color: var(--muted); font-size: 13.5px; }

/* ---------- Problem list ---------- */
.problem-list { display: grid; gap: 18px; }

.problem {
  padding: 22px;
  border-radius: var(--radius);
  background: linear-gradient(180deg, var(--card-2), var(--card));
  box-shadow: inset 0 0 0 1px var(--line);
}
.problem:target { box-shadow: inset 0 0 0 1px var(--accent), var(--shadow); }

.problem-head {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  margin-bottom: 4px;
}
.problem-num {
  font-family: var(--mono);
  font-size: 13px;
  color: var(--muted);
}
.problem h3 {
  margin: 0;
  font-size: 20px;
  letter-spacing: -.2px;
}
.problem h3 a { color: inherit; }

.badges { display: flex; flex-wrap: wrap; gap: 8px; margin: 10px 0 4px; }

.badge {
  padding: 3px 11px;
  border-radius: 999px;
  font-size: 12.5px;
  font-weight: 600;
  background: var(--bg-soft);
  box-shadow: inset 0 0 0 1px var(--line);
  color: var(--muted);
  text-transform: uppercase;
  letter-spacing: .4px;
}
.badge.diff-easy { color: #0b1b12; background: var(--easy); box-shadow: none; }
.badge.diff-medium { color: #1b1705; background: var(--medium); box-shadow: none; }
.badge.diff-hard { color: #fff; background: var(--hard); box-shadow: none; }
.badge.topic { text-transform: none; letter-spacing: 0; font-weight: 500; }

.problem p { margin: 10px 0; }
.problem .sources { font-size: 14px; color: var(--muted); }

.limits {
  margin: 14px 0;
  padding: 12px 16px;
  border-radius: 10px;
  background: var(--bg-soft);
  box-shadow: inset 0 0 0 1px var(--line);
  font-size: 14.5px;
  color: var(--muted);
}
.limits strong { color: var(--text); }

/* ---------- Examples ---------- */
.example { margin: 14px 0; }
.example-title { font-size: 14px; font-weight: 600; color: var(--muted); }

pre {
  margin: 6px 0 0;
  padding: 14px 16px;
  overflow-x: auto;
  border-radius: 10px;
  background: #0b0f1c;
  box-shadow: inset 0 0 0 1px var(--line);
  font-family: var(--mono);
  font-size: 13.5px;
  line-height: 1.6;
  color: #d7e0f5;
}
code { font-family: var(--mono); font-size: .92em; }
p code, li code, td code {
  padding: 2px 6px;
  border-radius: 6px;
  background: #0b0f1c;
  box-shadow: inset 0 0 0 1px var(--line);
}

/* ---------- Details: hint / solution ---------- */
details {
  margin-top: 14px;
  border-radius: 10px;
  background: var(--bg-soft);
  box-shadow: inset 0 0 0 1px var(--line);
  overflow: hidden;
}
details > summary {
  cursor: pointer;
  list-style: none;
  padding: 12px 16px;
  font-weight: 600;
  font-size: 14.5px;
  display: flex;
  align-items: center;
  gap: 8px;
}
details > summary::-webkit-details-marker { display: none; }
details > summary::before {
  content: "▸";
  color: var(--accent);
  transition: transform .15s ease;
}
details[open] > summary::before { transform: rotate(90deg); }
details > summary:hover { color: #fff; }
details .details-body { padding: 0 16px 16px; font-size: 15px; }
details.hint { box-shadow: inset 0 0 0 1px rgba(241, 196, 15, .35); }
details.solution { box-shadow: inset 0 0 0 1px rgba(91, 140, 255, .35); }
details.solution .details-body { padding-top: 4px; }

.complexity {
  margin: 12px 0 0;
  font-size: 14px;
  color: var(--muted);
}
.complexity code { color: var(--text); }

ul.checklist { margin: 12px 0 0; padding-left: 20px; }
ul.checklist li { margin-bottom: 6px; }

/* ---------- Table (методичка) ---------- */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 16px 0;
  font-size: 15px;
}
th, td {
  padding: 10px 12px;
  text-align: left;
  border-bottom: 1px solid var(--line);
}
th { color: var(--muted); font-size: 13.5px; text-transform: uppercase; letter-spacing: .4px; }
tbody tr:hover { background: var(--card); }

.note {
  padding: 14px 18px;
  margin: 18px 0;
  border-radius: 10px;
  background: rgba(91, 140, 255, .1);
  box-shadow: inset 0 3px 0 0 var(--accent);
  font-size: 15px;
}
.note strong { color: #fff; }

/* ---------- Pager ---------- */
.pager {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 12px;
  margin: 32px 0 8px;
}
.pager a {
  padding: 10px 16px;
  border-radius: 10px;
  background: var(--card);
  box-shadow: inset 0 0 0 1px var(--line);
  font-size: 14.5px;
}
.pager a:hover { text-decoration: none; box-shadow: inset 0 0 0 1px var(--accent); }

/* ---------- Footer ---------- */
.site-footer {
  margin-top: 48px;
  padding: 24px 0 32px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 14px;
}
.site-footer .container {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 20px;
  align-items: center;
  justify-content: space-between;
}

/* ---------- Responsive ---------- */
@media (max-width: 640px) {
  .site-header .container { min-height: 0; padding-block: 12px; }
  .site-nav { margin-left: 0; width: 100%; overflow-x: auto; }
  .hero { padding-top: 36px; }
  .problem { padding: 18px; }
}