:root {
  --ink: #18212f;
  --muted: #5d6878;
  --paper: #fff9ea;
  --panel: #fffdf6;
  --accent: #9b4d00;
  --gold: #f6c453;
  --line: #e7ddc4;
  --console: #172231;
  --console-text: #fff7df;
  --green: #087f5b;
  --sidebar-width: 17rem;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: "Avenir Next", Avenir, "Trebuchet MS", Arial, sans-serif;
  line-height: 1.5;
}

button,
textarea {
  font: inherit;
}

.boot-message {
  margin: 4rem auto;
  max-width: 30rem;
  text-align: center;
}

.shell {
  display: grid;
  grid-template-columns: var(--sidebar-width) minmax(0, 1fr);
  min-height: 100vh;
}

.sidebar {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100vh;
  overflow-y: auto;
  padding: 1.5rem 1rem;
  background: var(--ink);
  color: #f4eeda;
}

.brand {
  margin-bottom: 1rem;
  padding: 0 0.5rem 1.25rem;
  border-bottom: 1px solid rgb(244 238 218 / 15%);
}

.brand-title {
  margin: 0;
  font-size: 1.15rem;
  font-weight: 800;
}

.brand-sub,
.nav-part-title {
  text-transform: uppercase;
  letter-spacing: 0.09em;
}

.brand-sub {
  margin: 0.15rem 0 0;
  color: var(--gold);
  font-size: 0.72rem;
}

.nav-part-title {
  margin: 0 0.5rem 0.45rem;
  color: rgb(244 238 218 / 55%);
  font-size: 0.68rem;
}

.chapter-list {
  margin: 0;
  padding: 0;
  list-style: none;
}

.nav-link {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.45rem 0.55rem;
  border-radius: 7px;
  color: #f4eeda;
  font-size: 0.88rem;
  text-decoration: none;
}

.nav-link:hover {
  background: rgb(244 238 218 / 8%);
}

.nav-link.active {
  background: var(--gold);
  color: var(--ink);
  font-weight: 750;
}

.nav-num {
  width: 1.25rem;
  text-align: right;
}

.nav-dot {
  width: 7px;
  height: 7px;
  margin-left: auto;
  border-radius: 50%;
  background: #46c67c;
}

.content {
  min-width: 0;
  max-width: 92rem;
  padding: 2.5rem clamp(1.25rem, 4vw, 3.5rem) 4rem;
}

.chapter-head {
  margin-bottom: 1.5rem;
  padding-bottom: 1.15rem;
  border-bottom: 2px solid var(--ink);
}

.chapter-kicker {
  margin: 0 0 0.35rem;
  color: var(--accent);
  font-size: 0.75rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.chapter-head h1 {
  margin: 0;
  font-size: clamp(2rem, 4vw, 2.75rem);
  letter-spacing: -0.035em;
  line-height: 1.05;
}

.chapter-lede {
  max-width: 48rem;
  margin: 0 0 1rem;
  color: var(--muted);
}

.runtime-note {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.55rem;
  max-width: 52rem;
  margin: 0 0 2rem;
  padding: 0.65rem 0.85rem;
  border: 1px solid #cbded6;
  border-radius: 8px;
  background: #edf8f3;
  color: #315c4c;
  font-size: 0.82rem;
}

.runtime-note span:last-child::before {
  content: "·";
  margin-right: 0.55rem;
}

.runtime-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--green);
}

.example {
  margin: 0 0 2rem;
  padding: 1.25rem;
  border: 2px solid var(--ink);
  border-radius: 12px;
  background: var(--panel);
  box-shadow: 6px 6px 0 rgb(24 33 47 / 10%);
  scroll-margin-top: 1.5rem;
}

.example-head {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 0.45rem;
}

.example-head h2 {
  margin: 0 0 0.4rem;
  font-size: 1.25rem;
  line-height: 1.2;
}

.chip {
  display: inline-block;
  padding: 0.15rem 0.6rem;
  border: 1px solid #f0d49a;
  border-radius: 999px;
  background: #fdeccd;
  color: var(--accent);
  font-size: 0.7rem;
  font-weight: 800;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.example-intro {
  max-width: 48rem;
  margin: 0 0 1rem;
  color: var(--muted);
}

.copy-button,
.reset-button,
.run-button {
  border: 1.5px solid var(--ink);
  border-radius: 7px;
  cursor: pointer;
  font-weight: 700;
}

.copy-button,
.reset-button {
  background: transparent;
}

.copy-button {
  flex: none;
  padding: 0.35rem 0.75rem;
  font-size: 0.8rem;
}

.copy-button:hover,
.reset-button:hover {
  background: #fdeccd;
}

.runner {
  display: grid;
  grid-template-columns: minmax(0, 1.05fr) minmax(18rem, 0.95fr);
  min-height: 24rem;
  overflow: hidden;
  border: 2px solid var(--ink);
  border-radius: 9px;
}

.editor-pane,
.console-pane {
  display: flex;
  min-width: 0;
  flex-direction: column;
}

.editor-pane {
  border-right: 2px solid var(--ink);
  background: #fffcf4;
}

.console-pane {
  background: var(--console);
  color: var(--console-text);
}

.pane-head {
  display: flex;
  min-height: 2.6rem;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  padding: 0.55rem 0.75rem;
  border-bottom: 1px solid #d9ceb5;
  color: var(--muted);
  font-size: 0.74rem;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.console-head {
  border-color: rgb(255 255 255 / 12%);
  color: #c8d0dc;
}

.runtime {
  color: #aeb8c5;
  font-size: 0.63rem;
  font-weight: 600;
  letter-spacing: 0;
  text-align: right;
  text-transform: none;
}

.runtime.ready {
  color: #8de4bd;
}

.runtime.error {
  color: #ffaaa5;
}

.reset-button {
  padding: 0.2rem 0.55rem;
  color: var(--ink);
  font-size: 0.7rem;
}

textarea {
  width: 100%;
  min-height: 21.4rem;
  flex: 1;
  resize: vertical;
  padding: 1rem;
  border: 0;
  outline: 0;
  background: #fffcf4;
  color: var(--ink);
  font-family: Menlo, Consolas, "Liberation Mono", monospace;
  font-size: 0.9rem;
  line-height: 1.55;
  tab-size: 4;
}

.console-pane pre {
  min-height: 21.4rem;
  flex: 1;
  margin: 0;
  padding: 1rem;
  overflow: auto;
  color: var(--console-text);
  font-family: Menlo, Consolas, "Liberation Mono", monospace;
  font-size: 0.9rem;
  line-height: 1.55;
  white-space: pre-wrap;
}

.console-pane pre.error-output {
  color: #ffb7b1;
}

.runner-actions {
  display: flex;
  align-items: center;
  gap: 0.8rem;
  margin-top: 0.85rem;
}

.run-button {
  padding: 0.55rem 1rem;
  background: var(--gold);
  color: var(--ink);
}

.run-button:hover:not(:disabled) {
  background: #ffd773;
}

.run-button:disabled {
  cursor: wait;
  opacity: 0.7;
}

.shortcut {
  color: var(--muted);
  font-size: 0.75rem;
}

@media (max-width: 850px) {
  .shell {
    display: block;
  }

  .sidebar {
    position: static;
    width: auto;
    height: auto;
  }

  .brand {
    padding-bottom: 0.8rem;
  }

  .runner {
    grid-template-columns: 1fr;
  }

  .editor-pane {
    border-right: 0;
    border-bottom: 2px solid var(--ink);
  }
}

@media (max-width: 520px) {
  .content {
    padding: 1.5rem 0.8rem 3rem;
  }

  .example {
    padding: 0.85rem;
  }

  .example-head {
    display: block;
  }

  .copy-button {
    margin-top: 0.75rem;
  }

  .runner {
    min-height: 0;
  }

  textarea,
  .console-pane pre {
    min-height: 18rem;
    font-size: 0.82rem;
  }
}