:root {
  --bg: #ffffff;
  --fg: #111111;
  --muted: #6b7280;
  --faint: #9ca3af;
  --line: #ececec;
  --line-strong: #e0e0e0;
  --hover: #f6f6f6;
  --active: #f0f0f0;
  --sidebar-w: 290px;
  --mono: ui-monospace, "SF Mono", "JetBrains Mono", "Fira Code", Menlo, Consolas, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Inter, Roboto, Helvetica, Arial, sans-serif;
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }

html, body {
  margin: 0;
  height: 100%;
  overflow: hidden; /* only #main scrolls — prevents a second outer scrollbar */
  background: var(--bg);
  color: var(--fg);
  font-family: var(--sans);
  font-size: 14px;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

/* Black selection highlight everywhere */
::selection { background: #000; color: #fff; }
::-moz-selection { background: #000; color: #fff; }

body { display: flex; }

a { color: inherit; text-decoration: none; }

/* ---------- Sidebar ---------- */
#sidebar {
  width: var(--sidebar-w);
  min-width: var(--sidebar-w);
  height: 100vh;
  position: sticky;
  top: 0;
  border-right: 1px solid var(--line);
  display: flex;
  flex-direction: column;
  background: var(--bg);
}

.brand {
  padding: 16px 12px 14px 20px;
  border-bottom: 1px solid var(--line);
  display: flex;
  align-items: center;
  gap: 6px;
  flex-shrink: 0;
}
.brand a { display: flex; flex-direction: column; gap: 2px; flex: 1; min-width: 0; overflow: hidden; }
.brand-name {
  font-weight: 620;
  font-size: 14px;
  letter-spacing: -0.01em;
}
.brand-sub {
  font-size: 11px;
  color: var(--faint);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

#filter-wrap { padding: 12px 14px; border-bottom: 1px solid var(--line); }
#filter {
  width: 100%;
  border: 1px solid var(--line-strong);
  border-radius: 7px;
  padding: 7px 10px;
  font-size: 13px;
  font-family: var(--sans);
  color: var(--fg);
  outline: none;
  background: var(--bg);
}
#filter:focus { border-color: #c4c4c4; }
#filter::placeholder { color: var(--faint); }

#nav { flex: 1; overflow-y: auto; padding: 8px 0 24px; }

.group { margin-top: 4px; }

.group-label,
.subgroup-label {
  display: flex;
  justify-content: space-between;
  align-items: center;
  cursor: pointer;
  user-select: none;
}
.group-label {
  padding: 12px 16px 6px 20px;
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.07em;
  color: var(--faint);
}
.group-label:hover { color: #888; }

/* Shared right-side container: count + chevron */
.label-right { display: flex; align-items: center; gap: 5px; }
.count { font-weight: 500; font-size: 10px; color: var(--line-strong); }

/* Chevron */
.chevron {
  width: 12px;
  height: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: transform 0.15s ease;
  flex-shrink: 0;
  color: var(--line-strong);
}
.chevron::after { content: "▾"; font-size: 9px; }

/* Rotate chevron when collapsed */
.group.collapsed > .group-label .chevron { transform: rotate(-90deg); }
.subgroup.collapsed > .subgroup-label .chevron { transform: rotate(-90deg); }

/* Hide children when collapsed */
.group.collapsed > .item,
.group.collapsed > .subgroup { display: none; }
.subgroup.collapsed > .item { display: none; }

/* CSES sub-category groups */
.subgroup { margin-top: 0; }
.subgroup-label {
  padding: 7px 16px 5px 26px;
  font-size: 10.5px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--faint);
  border-top: 1px solid var(--line);
}
.subgroup-label:hover { color: #888; }
.subgroup > .item { padding-left: 34px; }

/* Nav items */
.item {
  display: block;
  padding: 7px 20px;
  font-size: 13.5px;
  font-family: var(--mono);
  color: #333;
  cursor: pointer;
  border-left: 2px solid transparent;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.item:hover { background: var(--hover); }
.item.active {
  background: var(--active);
  border-left-color: #111;
  color: #000;
  font-weight: 500;
}

/* Two-line item (CF with problem name) */
.item--rich {
  white-space: normal;
  overflow: visible;
  padding-top: 6px;
  padding-bottom: 6px;
}
.item-name {
  display: block;
  font-family: var(--sans);
  font-size: 13px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  color: #333;
}
.item-id {
  display: block;
  font-family: var(--mono);
  font-size: 10.5px;
  color: var(--muted);
  margin-top: 2px;
}
.item--rich.active .item-name { color: #000; }
.item--rich.active .item-id { color: var(--muted); }

/* CSES items use sans (display names, not ids) */
.item[data-key*="cses/"] {
  font-family: var(--sans);
  font-size: 13px;
}
.subgroup > .item {
  font-family: var(--sans);
  font-size: 13px;
  padding-left: 34px;
}

.side-foot {
  padding: 12px 20px;
  border-top: 1px solid var(--line);
  font-size: 11px;
  color: var(--faint);
}

/* ---------- Main ---------- */
#main {
  flex: 1;
  min-width: 0;
  height: 100vh;
  overflow-y: auto;
}

.state {
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 40px;
}
/* Loading hint sits near the top instead of floating in a tall empty void */
#loading {
  height: auto;
  justify-content: flex-start;
  padding: 28px 40px;
}
.state-inner { max-width: 420px; text-align: center; }
.state-inner h1 { font-size: 22px; font-weight: 640; margin: 0 0 10px; letter-spacing: -0.02em; }
.state-inner p { margin: 4px 0; color: var(--muted); line-height: 1.6; }
.muted { color: var(--faint) !important; font-size: 13px; }

#content { max-width: 880px; margin: 0 auto; padding: 0 40px 100px; }

#content-head {
  position: sticky;
  top: 0;
  background: var(--bg);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 22px 0 16px;
  border-bottom: 1px solid var(--line);
  z-index: 5;
}
.crumbs { font-family: var(--mono); font-size: 14px; display: flex; align-items: center; gap: 8px; }
.crumbs .sep { color: var(--faint); }
#c-platform { color: var(--muted); }
#c-id { font-weight: 600; }

.ghost-btn {
  border: 1px solid var(--line-strong);
  background: var(--bg);
  color: #333;
  border-radius: 7px;
  padding: 6px 11px;
  font-size: 12.5px;
  font-family: var(--sans);
  cursor: pointer;
  white-space: nowrap;
}
.ghost-btn:hover { background: var(--hover); border-color: #c4c4c4; }
.ghost-btn:active { background: var(--active); }

/* ---------- Markdown description ---------- */
.markdown-body { padding: 28px 0 8px; line-height: 1.7; color: #1c1c1c; font-size: 14.5px; }
.markdown-body h1 { font-size: 24px; font-weight: 660; letter-spacing: -0.02em; margin: 0 0 4px; }
.markdown-body h2 { font-size: 17px; font-weight: 620; margin: 28px 0 10px; }
.markdown-body h3 { font-size: 15px; font-weight: 620; margin: 22px 0 8px; }
.markdown-body p { margin: 12px 0; }
.markdown-body a { text-decoration: underline; text-underline-offset: 2px; text-decoration-color: var(--line-strong); }
.markdown-body a:hover { text-decoration-color: #000; }
.markdown-body ul, .markdown-body ol { padding-left: 22px; margin: 12px 0; }
.markdown-body li { margin: 5px 0; }
.markdown-body code {
  font-family: var(--mono);
  font-size: 0.88em;
  background: #f3f3f3;
  padding: 2px 5px;
  border-radius: 4px;
}
.markdown-body pre {
  background: #fafafa;
  border: 1px solid var(--line);
  border-radius: 9px;
  padding: 14px 16px;
  overflow-x: auto;
}
.markdown-body pre code { background: none; padding: 0; font-size: 13px; }
.markdown-body blockquote {
  margin: 14px 0;
  padding: 2px 16px;
  border-left: 3px solid var(--line-strong);
  color: var(--muted);
}
.markdown-body table { border-collapse: collapse; margin: 14px 0; font-size: 13.5px; }
.markdown-body th, .markdown-body td { border: 1px solid var(--line-strong); padding: 6px 12px; text-align: left; }
.markdown-body th { background: #fafafa; }
.markdown-body img { max-width: 100%; }
.markdown-body hr { border: none; border-top: 1px solid var(--line); margin: 28px 0; }

/* ---------- Editor / IDE panel ---------- */
#editor {
  margin-top: 28px;
  border: 1px solid var(--line-strong);
  border-radius: 11px;
  overflow: hidden;
  background: var(--bg);
}
.editor-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 9px 14px;
  border-bottom: 1px solid var(--line);
  background: #fbfbfb;
}
.file-name { font-family: var(--mono); font-size: 12.5px; color: var(--muted); }
.editor-bar .ghost-btn { padding: 4px 10px; font-size: 12px; }

.editor-body { overflow-x: auto; }
.editor-body pre { margin: 0; }
.editor-body code {
  display: block;
  font-family: var(--mono);
  font-size: 13px;
  line-height: 1.65;
  tab-size: 4;
}

/* line-numbered rows */
.code-line { display: flex; }
.code-line:hover { background: #fafafa; }
.ln {
  flex: 0 0 auto;
  width: 3.2em;
  padding: 0 14px 0 0;
  text-align: right;
  color: var(--faint);
  user-select: none;
  -webkit-user-select: none;
  font-variant-numeric: tabular-nums;
}
.lc { flex: 1; padding-right: 18px; white-space: pre; }

/* ---------- Sidebar collapse toggle button ---------- */
#sidebar-toggle {
  flex-shrink: 0;
  background: none;
  border: none;
  font-size: 16px;
  line-height: 1;
  cursor: pointer;
  color: var(--faint);
  padding: 4px 5px;
  border-radius: 5px;
  display: flex;
  align-items: center;
  justify-content: center;
}
#sidebar-toggle:hover { background: var(--hover); color: var(--fg); }

/* When collapsed, sidebar narrows to a thin strip showing only the toggle */
#sidebar { transition: width 0.18s ease, min-width 0.18s ease; }

body.sidebar-collapsed #sidebar {
  width: 40px;
  min-width: 40px;
}
body.sidebar-collapsed #filter-wrap,
body.sidebar-collapsed #nav,
body.sidebar-collapsed #side-foot { display: none; }
body.sidebar-collapsed .brand {
  padding: 14px 0;
  justify-content: center;
  border-bottom: none;
}
body.sidebar-collapsed .brand > a { display: none; }

/* ---------- mobile ---------- */
#menu-toggle {
  display: none;
  position: fixed;
  top: 12px;
  left: 12px;
  z-index: 50;
  width: 38px;
  height: 38px;
  border: 1px solid var(--line-strong);
  background: var(--bg);
  border-radius: 9px;
  font-size: 18px;
  line-height: 1;
  cursor: pointer;
}

@media (max-width: 760px) {
  #menu-toggle { display: block; }
  #sidebar-toggle { display: none !important; }
  #sidebar {
    position: fixed;
    z-index: 40;
    transform: translateX(-100%);
    transition: transform 0.18s ease;
    box-shadow: 0 0 0 100vmax rgba(0,0,0,0);
  }
  body.nav-open #sidebar { transform: translateX(0); box-shadow: 40px 0 80px rgba(0,0,0,0.12); }
  #content { padding: 56px 20px 80px; }
  #content-head { padding-top: 8px; }
}