:root {
  --bg: #121410;
  --bg-side: #181b14;
  --bg-raise: #1e2218;
  --bg-code: #0c0d0a;
  --line: rgba(236, 234, 223, 0.12);
  --line-strong: rgba(236, 234, 223, 0.22);
  --text: #eceadf;
  --muted: #a8aa9c;
  --faint: #74786a;
  --acid: #e2f15a;
  --ink: #16180d;
  --ok: #c6f08a;
  --ok-bg: #141a10;
  --bad: #ff8d78;
  --bad-bg: #211410;
  --warn: #ffc56b;
  --peach: #f0b27a;
  --blue: #a9cffc;
  --sans: Manrope, "Avenir Next", "Segoe UI", sans-serif;
  --display: Unbounded, Manrope, "Avenir Next", sans-serif;
  --mono: "IBM Plex Mono", "SF Mono", ui-monospace, Menlo, Consolas, monospace;
  color-scheme: dark;
}

* { box-sizing: border-box; }
html, body { margin: 0; height: 100%; }
body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--sans);
  font-size: 16.5px;
  line-height: 1.55;
}
::selection { background: var(--acid); color: var(--ink); }
button, textarea { font: inherit; color: inherit; }
button { cursor: pointer; }
:focus-visible { outline: 2px solid var(--acid); outline-offset: 2px; }
* { scrollbar-width: thin; scrollbar-color: #3a3d32 transparent; }

.topbar {
  position: fixed;
  z-index: 5;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: #2a2d24;
}
.topbar-fill {
  height: 100%;
  width: 0;
  background: var(--acid);
  transition: width 0.25s ease;
}

.layout {
  display: grid;
  grid-template-columns: 300px 1fr;
  height: 100vh;
  height: 100dvh;
}

.sidebar {
  display: flex;
  flex-direction: column;
  min-height: 0;
  background: var(--bg-side);
  border-right: 1px solid var(--line);
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 22px 18px 0;
  background: transparent;
  border: 0;
  text-align: left;
}
.brand-mark {
  display: grid;
  place-items: center;
  width: 34px;
  height: 34px;
  border-radius: 9px;
  background: var(--acid);
  color: var(--ink);
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 500;
}
.brand-name {
  font-family: var(--display);
  font-size: 22px;
  letter-spacing: -0.04em;
  line-height: 1;
}
.brand-sub {
  margin: 8px 18px 0;
  color: var(--faint);
  font-family: var(--mono);
  font-size: 12px;
}
.progress { padding: 18px 18px 8px; }
.progress-row {
  display: flex;
  justify-content: space-between;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 12px;
  margin-bottom: 8px;
}
.progress-track {
  height: 4px;
  border-radius: 99px;
  background: #2c2f26;
  overflow: hidden;
}
.progress-fill {
  height: 100%;
  width: 0;
  background: var(--acid);
}

.side-nav {
  overflow: auto;
  padding: 8px 10px 12px;
  display: flex;
  flex-direction: column;
  gap: 2px;
}
.mod-btn {
  display: grid;
  grid-template-columns: 28px 1fr auto;
  gap: 8px;
  align-items: center;
  width: 100%;
  padding: 8px 8px;
  border: 0;
  border-radius: 8px;
  background: transparent;
  text-align: left;
}
.mod-btn:hover { background: rgba(226, 241, 90, 0.06); }
.mod-btn.active { background: rgba(226, 241, 90, 0.1); }
.mod-num {
  font-family: var(--mono);
  font-size: 12px;
  color: var(--faint);
}
.mod-btn.active .mod-num,
.mod-btn.complete .mod-num { color: var(--acid); }
.mod-name { font-size: 14.5px; font-weight: 600; }
.mod-count {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--faint);
}
.side-links {
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: 0 10px 8px;
}
.side-link {
  border: 0;
  background: transparent;
  text-align: left;
  padding: 8px 8px;
  border-radius: 8px;
  color: var(--muted);
  font-size: 14px;
}
.side-link:hover, .side-link.active { background: rgba(226, 241, 90, 0.08); color: var(--text); }

.side-foot {
  margin-top: auto;
  padding: 12px 18px 16px;
  border-top: 1px solid var(--line);
}
.py-status {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 12px;
}
.dot {
  width: 8px;
  height: 8px;
  border-radius: 99px;
  background: var(--warn);
}
.dot.ok { background: var(--ok); }
.dot.bad { background: var(--bad); }
.dot.load { animation: pulse 1.2s infinite; }
@keyframes pulse {
  50% { opacity: 0.35; }
}
.linkish {
  margin-top: 8px;
  padding: 0;
  border: 0;
  background: none;
  color: var(--faint);
  font-size: 12px;
  text-decoration: underline;
  text-underline-offset: 3px;
}

.main {
  min-width: 0;
  overflow: auto;
  padding: 36px 48px 72px;
}
.main-inner { max-width: 980px; }

.kicker {
  margin: 0 0 8px;
  color: var(--acid);
  font-family: var(--mono);
  font-size: 12px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}
h1 {
  margin: 0;
  font-family: var(--display);
  font-weight: 500;
  font-size: 42px;
  letter-spacing: -0.045em;
  line-height: 1.12;
}
.outcome, .lead {
  max-width: 66ch;
  color: var(--muted);
  font-size: 17px;
}
.outcome { margin: 12px 0 0; }
.lead { margin: 16px 0 0; color: var(--text); }

.steps {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 12px;
  margin: 28px 0 0;
  padding: 0;
  list-style: none;
}
.steps li {
  padding: 14px 14px 16px;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.02);
  color: var(--muted);
  font-size: 14.5px;
}
.steps span {
  display: block;
  margin-bottom: 8px;
  color: var(--acid);
  font-family: var(--mono);
  font-size: 12px;
}

.topic-list {
  display: flex;
  flex-direction: column;
  margin-top: 28px;
  border-top: 1px solid var(--line);
}
.topic {
  display: grid;
  grid-template-columns: 42px 1fr auto;
  gap: 12px;
  align-items: baseline;
  width: 100%;
  padding: 12px 0;
  border: 0;
  border-bottom: 1px solid var(--line);
  background: transparent;
  text-align: left;
}
.topic:hover .topic-title { color: var(--acid); }
.topic-num { font-family: var(--mono); color: var(--faint); font-size: 12px; }
.topic-title { font-weight: 700; }
.topic-out { color: var(--faint); font-size: 13px; }

.actions-row { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 26px; }

.btn {
  height: 42px;
  padding: 0 16px;
  border-radius: 10px;
  border: 1px solid var(--line-strong);
  background: transparent;
  font-weight: 700;
}
.btn:hover { border-color: var(--text); }
.btn.primary { background: var(--acid); color: var(--ink); border-color: var(--acid); }
.btn.primary:hover { filter: brightness(1.05); }
.btn:disabled { opacity: 0.45; cursor: wait; }
.btn.small { height: 30px; padding: 0 10px; font-size: 13px; font-weight: 600; }

.lesson-block { margin-top: 28px; }
.eyebrow {
  margin: 0 0 10px;
  color: var(--acid);
  font-family: var(--mono);
  font-size: 12px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}
.prose { max-width: 68ch; }
.prose p { margin: 0 0 12px; }
.prose strong { font-weight: 700; }
.prose code, .task-copy code, .fold code {
  font-family: var(--mono);
  font-size: 0.88em;
  padding: 1px 5px;
  border-radius: 5px;
  background: #26291f;
  color: var(--peach);
}
pre.code {
  margin: 0 0 14px;
  padding: 14px 16px;
  overflow: auto;
  border-radius: 12px;
  background: var(--bg-code);
  border: 1px solid var(--line);
  font-family: var(--mono);
  font-size: 13.5px;
  line-height: 1.6;
  color: #dddccf;
}
.pitfall {
  max-width: 68ch;
  margin-top: 8px;
  padding: 12px 14px;
  border-left: 3px solid var(--bad);
  background: rgba(255, 141, 120, 0.06);
  border-radius: 0 10px 10px 0;
}
.pitfall .eyebrow { color: var(--bad); }
.pitfall p { margin: 0 0 8px; }
.result ul { margin: 8px 0 0; padding-left: 18px; }
.result li + li { margin-top: 6px; }

.task-head {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  align-items: end;
  margin-top: 34px;
}
.pills { display: flex; flex-wrap: wrap; gap: 8px; }
.pill {
  min-width: 38px;
  height: 38px;
  padding: 0 10px;
  border-radius: 10px;
  border: 1px solid var(--line-strong);
  background: transparent;
  font-family: var(--mono);
  font-size: 13px;
}
.pill.on { border-color: var(--acid); color: var(--acid); }
.pill.done { background: var(--acid); border-color: var(--acid); color: var(--ink); }
.pill.done.on { box-shadow: inset 0 0 0 2px var(--ink); }
.task-count { color: var(--faint); font-family: var(--mono); font-size: 12px; }
.task-title { margin: 16px 0 8px; font-size: 28px; letter-spacing: -0.03em; font-weight: 700; }
.task-copy { max-width: 68ch; }
.task-copy p { margin: 0 0 10px; }

.sample {
  max-width: 760px;
  margin: 14px 0;
  padding: 12px 14px;
  border-radius: 12px;
  border: 1px dashed var(--line-strong);
}
.sample-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
}
.sample pre, .diff pre, .trace {
  margin: 0;
  white-space: pre-wrap;
  font-family: var(--mono);
  font-size: 13px;
  line-height: 1.5;
}
.sample .more { margin: 8px 0 0; color: var(--faint); font-size: 13px; }

.fold { margin: 8px 0; }
.fold summary {
  width: fit-content;
  color: var(--muted);
  font-size: 14px;
  cursor: pointer;
}
.fold summary:hover { color: var(--text); }
.fold .inner { margin-top: 8px; max-width: 760px; }

.editor-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 16px;
  padding: 0 2px 8px;
  color: var(--faint);
  font-family: var(--mono);
  font-size: 12px;
}
.CodeMirror {
  height: 320px;
  border-radius: 12px;
  border: 1px solid var(--line-strong);
  font-family: var(--mono);
  font-size: 14.5px;
  line-height: 1.55;
}
.cm-s-razgon.CodeMirror { background: var(--bg-code); color: var(--text); }
.cm-s-razgon .CodeMirror-gutters {
  background: var(--bg-code);
  border-right: 1px solid var(--line);
}
.cm-s-razgon .CodeMirror-linenumber { color: #5e6156; }
.cm-s-razgon .CodeMirror-cursor { border-left: 2px solid var(--acid); }
.cm-s-razgon .CodeMirror-selected { background: rgba(226, 241, 90, 0.16); }
.cm-s-razgon .CodeMirror-activeline-background { background: rgba(226, 241, 90, 0.04); }
.cm-s-razgon .cm-keyword { color: var(--acid); }
.cm-s-razgon .cm-builtin { color: var(--blue); }
.cm-s-razgon .cm-string { color: var(--peach); }
.cm-s-razgon .cm-number { color: var(--blue); }
.cm-s-razgon .cm-comment { color: #727568; font-style: italic; }
.cm-s-razgon .cm-def { color: var(--ok); }
.cm-s-razgon .cm-operator { color: var(--text); }
.cm-s-razgon .cm-variable { color: var(--text); }

.stdin-label {
  display: block;
  margin: 14px 0 6px;
  color: var(--faint);
  font-family: var(--mono);
  font-size: 12px;
}
.stdin {
  width: 100%;
  min-height: 88px;
  padding: 12px;
  border-radius: 12px;
  border: 1px solid var(--line-strong);
  background: var(--bg-code);
  font-family: var(--mono);
  font-size: 14px;
  resize: vertical;
}

.runbar {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
  margin-top: 12px;
}
.keys { color: var(--faint); font-family: var(--mono); font-size: 12px; }
.next-link {
  margin-left: auto;
  border: 0;
  background: none;
  color: var(--muted);
  font-weight: 700;
  padding: 0 4px;
}
.next-link:hover { color: var(--acid); }

.result {
  margin-top: 16px;
  padding: 14px 16px;
  border-radius: 12px;
  border: 1px solid var(--line);
  background: #14160f;
  min-height: 72px;
}
.result.ok { background: var(--ok-bg); border-color: rgba(198, 240, 138, 0.35); }
.result.bad { background: var(--bad-bg); border-color: rgba(255, 141, 120, 0.4); }
.result h3 { margin: 0 0 8px; font-size: 18px; }
.result p { margin: 0 0 8px; }
.result .quiet { color: var(--muted); }
.diff {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-top: 8px;
}
.trace {
  padding: 10px 12px;
  border-radius: 8px;
  background: #100e0c;
  color: #ffd0c6;
}

.banner {
  margin-bottom: 16px;
  padding: 12px 14px;
  border-radius: 10px;
  background: #2a2214;
  color: var(--warn);
}

@media (max-width: 960px) {
  .layout { grid-template-columns: 1fr; height: auto; min-height: 100vh; }
  .sidebar { border-right: 0; border-bottom: 1px solid var(--line); }
  .side-nav { flex-direction: row; overflow-x: auto; }
  .mod-btn { width: auto; white-space: nowrap; }
  .side-foot { display: none; }
  .main { padding: 24px 18px 48px; }
  h1 { font-size: 34px; }
  .steps, .sample-grid, .diff { grid-template-columns: 1fr; }
}

@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; animation: none !important; scroll-behavior: auto !important; }
}