:root {
  --sidebar-width: 280px;
  --bg: #0f1115;
  --bg-elevated: #161a22;
  --border: #262b36;
  --text: #e6e9ef;
  --text-muted: #9aa3b2;
  --accent: #6ea8fe;
  --accent-soft: rgba(110, 168, 254, 0.12);
  --code-bg: #0d1117;
  --yes: #3fb950;
  --no: #f85149;
}

* {
  box-sizing: border-box;
}

html, body {
  height: 100%;
}

body {
  background: var(--bg);
  color: var(--text);
  font-family: "Segoe UI", Roboto, -apple-system, BlinkMacSystemFont, sans-serif;
}

/* ---------- Sidebar ---------- */

#sidebar {
  width: var(--sidebar-width);
  min-height: 100vh;
  background: var(--bg-elevated);
  border-right: 1px solid var(--border);
  position: sticky;
  top: 0;
  overflow-y: auto;
}

.sidebar-header {
  padding: 1.25rem 1rem;
  border-bottom: 1px solid var(--border);
}

.sidebar-header .brand {
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: .02em;
}

.sidebar-header .brand-sub {
  color: var(--text-muted);
  font-size: .78rem;
}

.category-group {
  border-bottom: 1px solid var(--border);
}

.category-toggle {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  padding: .8rem 1rem;
  background: none;
  border: none;
  color: var(--text);
  font-weight: 600;
  font-size: .92rem;
  cursor: pointer;
  text-align: left;
}

.category-toggle:hover {
  background: rgba(255,255,255,0.03);
}

.category-toggle .chev {
  transition: transform .15s ease;
  color: var(--text-muted);
  font-size: .75rem;
}

.category-toggle[aria-expanded="true"] .chev {
  transform: rotate(90deg);
}

.category-toggle.disabled {
  cursor: default;
  color: var(--text-muted);
}

.category-toggle.disabled:hover {
  background: none;
}

.soon-badge {
  font-size: .62rem;
  font-weight: 600;
  letter-spacing: .04em;
  text-transform: uppercase;
  padding: .18rem .5rem;
  border-radius: 999px;
  background: rgba(255,255,255,0.06);
  color: var(--text-muted);
  border: 1px solid var(--border);
}

.challenge-list {
  list-style: none;
  margin: 0;
  padding: .25rem 0 .6rem;
}

.challenge-list .chal-link {
  display: flex;
  align-items: center;
  gap: .6rem;
  width: 100%;
  padding: .55rem 1rem .55rem 2.1rem;
  background: none;
  border: none;
  color: var(--text-muted);
  font-size: .86rem;
  text-align: left;
  cursor: pointer;
  border-left: 3px solid transparent;
}

.challenge-list .chal-link .idx {
  font-variant-numeric: tabular-nums;
  color: var(--text-muted);
  font-size: .78rem;
  width: 1.rem;
}

.challenge-list .chal-link:hover {
  background: rgba(255,255,255,0.03);
  color: var(--text);
}

.challenge-list .chal-link.active {
  background: var(--accent-soft);
  color: var(--accent);
  border-left-color: var(--accent);
  font-weight: 600;
}

/* ---------- Main content ---------- */

#main {
  flex: 1;
  min-width: 0;
}

.topbar {
  border-bottom: 1px solid var(--border);
  padding: .9rem 1.5rem;
  background: var(--bg-elevated);
  position: sticky;
  top: 0;
  z-index: 10;
}

.topbar .crumb {
  color: var(--text-muted);
  font-size: .82rem;
}

.topbar .crumb .current {
  color: var(--text);
  font-weight: 600;
}

.content-wrap {
  max-width: 1100px;
  margin: 0 auto;
  padding: 2rem 1.75rem 4rem;
}

.chal-title {
  font-weight: 800;
  font-size: 1.9rem;
  margin-bottom: .25rem;
}

.chal-lang-badge {
  display: inline-block;
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .03em;
  padding: .2rem .6rem;
  border-radius: 6px;
  background: rgba(222, 118, 78, 0.15);
  color: #f4936a;
  border: 1px solid rgba(222,118,78,0.3);
  margin-bottom: 1.25rem;
}

.writeup h2 {
  font-size: 1.25rem;
  font-weight: 700;
  margin-top: 2.2rem;
  margin-bottom: .9rem;
  padding-bottom: .4rem;
  border-bottom: 1px solid var(--border);
}

.writeup h3 {
  font-size: 1.02rem;
  font-weight: 700;
  margin-top: 1.5rem;
  margin-bottom: .6rem;
  color: var(--accent);
}

.writeup p {
  color: #c7cddb;
  line-height: 1.7;
}

.text-muted {
  color: var(--text-muted) !important;
}

.writeup blockquote {
  border-left: 3px solid var(--accent);
  padding: .4rem 1rem;
  margin: 1rem 0;
  background: var(--accent-soft);
  color: #c7cddb;
  border-radius: 0 6px 6px 0;
  font-style: italic;
}

.writeup ul, .writeup ol {
  color: #c7cddb;
  line-height: 1.7;
}

.writeup code:not(pre code) {
  background: rgba(255,255,255,0.08);
  padding: .12rem .4rem;
  border-radius: 4px;
  font-size: .85em;
  color: #f4936a;
}

.writeup pre {
  background: var(--code-bg) !important;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1rem 1.1rem;
  overflow-x: auto;
  margin-bottom: 1.1rem;
}

.writeup pre code {
  font-size: .85rem;
  line-height: 1.55;
  white-space: pre;
  word-wrap: normal;
  overflow-wrap: normal;
}

.writeup .ascii-block {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1rem 1.1rem;
  color: #9fd6a3;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: .85rem;
  overflow-x: auto;
  margin-bottom: 1.1rem;
  white-space: pre;
}

.writeup table {
  width: 100%;
  border-collapse: collapse;
  margin-bottom: 1.1rem;
  font-size: .88rem;
}

.writeup table th, .writeup table td {
  border: 1px solid var(--border);
  padding: .5rem .75rem;
  text-align: right;
}

.writeup table th {
  background: rgba(255,255,255,0.04);
  color: var(--text);
}

.writeup table td {
  color: #c7cddb;
}

.section-label {
  display: inline-flex;
  align-items: center;
  gap: .4rem;
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .06em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-top: 1.6rem;
  margin-bottom: .6rem;
}

.nav-footer {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
}

.nav-footer .btn {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  color: var(--text);
}

.nav-footer .btn:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.coming-soon-view {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 60vh;
  text-align: center;
  color: var(--text-muted);
}

.coming-soon-view .icon {
  font-size: 2.6rem;
  margin-bottom: 1rem;
  opacity: .6;
}

.coming-soon-view h2 {
  color: var(--text);
  font-size: 1.4rem;
  margin-bottom: .4rem;
}

#sidebarToggle {
  display: none;
}

@media (max-width: 900px) {
  #sidebarToggle {
    display: inline-flex;
  }

  #sidebar {
    position: fixed;
    left: 0;
    top: 0;
    z-index: 1050;
    transform: translateX(-100%);
    transition: transform .2s ease;
    box-shadow: 4px 0 24px rgba(0,0,0,0.4);
  }

  #sidebar.open {
    transform: translateX(0);
  }

  .sidebar-backdrop {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.5);
    z-index: 1040;
  }

  .sidebar-backdrop.show {
    display: block;
  }
}