*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg: #191c24;
  --bg-side: #14171e;
  --bg-elev: #1f232c;
  --bg-code: #12151b;
  --bg-hover: #252a34;
  --border: #2c313c;
  --border-soft: #252a33;
  --text: #d7dbe3;
  --muted: #9aa3b2;
  --dim: #7a8391;
  --accent: #7eb6c4;
  --accent-dim: rgba(126, 182, 196, 0.12);
  --accent-line: rgba(126, 182, 196, 0.38);
  --ok: #86c49a;
  --ok-dim: rgba(110, 190, 150, 0.14);
  --ok-line: #6ecb9a;
  --warn: #c4a574;
  --warn-dim: rgba(196, 165, 116, 0.12);
  --new-fg: #d5f0de;
  --old-fg: #8b939f;
  --radius: 8px;
  --side-w: 268px;
  --fs: 16.5px;
  --fs-code: 13.5px;
  --mono: "IBM Plex Mono", ui-monospace, monospace;
  --sans: Inter, system-ui, sans-serif;
}

html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--text);
  font-family: var(--sans);
  font-size: var(--fs);
  line-height: 1.55;
  min-height: 100vh;
}

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

code, kbd {
  font-family: var(--mono);
  font-size: 0.9em;
}

:not(pre) > code {
  background: var(--bg-elev);
  border: 1px solid var(--border-soft);
  border-radius: 4px;
  padding: 0.07em 0.38em;
  color: var(--text);
}

.page {
  display: grid;
  grid-template-columns: var(--side-w) 1fr;
  min-height: 100vh;
}

/* ── Sidebar ── */
.sidebar {
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
  background: var(--bg-side);
  border-right: 1px solid var(--border);
  padding: 1.45rem 0.85rem 2.5rem;
  display: flex;
  flex-direction: column;
}

.brand {
  padding: 0 0.55rem;
  margin-bottom: 1.15rem;
}

.brand a {
  color: var(--text);
  text-decoration: none;
  font-weight: 700;
  font-size: 1.02rem;
  letter-spacing: -0.03em;
}

.brand a:hover { color: var(--accent); text-decoration: none; }

.brand .sub {
  display: block;
  margin-top: 0.18rem;
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--dim);
}

.tut-label {
  padding: 0 0.55rem;
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.2rem;
}

.tut-title {
  padding: 0 0.55rem 1rem;
  font-size: 0.92rem;
  font-weight: 600;
  color: var(--text);
  line-height: 1.35;
  border-bottom: 1px solid var(--border);
  margin-bottom: 0.85rem;
}

.steps {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 0.12rem;
}

.steps a {
  display: grid;
  grid-template-columns: 1.6rem 1fr;
  gap: 0.35rem;
  align-items: baseline;
  padding: 0.42rem 0.55rem;
  border-radius: 6px;
  color: var(--muted);
  font-size: 13.5px;
  line-height: 1.35;
  text-decoration: none;
  border-left: 2px solid transparent;
}

.steps a:hover {
  color: var(--text);
  background: var(--bg-hover);
  text-decoration: none;
}

.steps a .n {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--dim);
}

.steps a.active {
  color: var(--accent);
  background: var(--accent-dim);
  border-left-color: var(--accent);
}

.steps a.active .n { color: var(--accent); }

.steps a.done { color: var(--text); }
.steps a.done .n { color: var(--ok); }

.steps .part {
  padding: 0.95rem 0.55rem 0.3rem;
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  color: var(--dim);
}

.steps .part:first-child { padding-top: 0; }

/* ── Main ── */
main {
  padding: 2.1rem 2.4rem 5.5rem;
  min-width: 0;
  max-width: 52rem;
}

.kicker {
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.45rem;
}

main h1 {
  font-size: 1.72rem;
  font-weight: 700;
  letter-spacing: -0.04em;
  line-height: 1.18;
  margin-bottom: 0.7rem;
}

.explain {
  color: var(--muted);
  margin-bottom: 0.7rem;
  max-width: 42rem;
}

.explain p + p { margin-top: 0.55rem; }
.explain strong { color: var(--text); font-weight: 600; }

/* A drawing in the explanation: inline SVG, theme colors through classes. */
.fig { margin: 1rem 0 1.1rem; text-align: center; }
.fig svg { width: 100%; max-width: 27rem; height: auto; }
.fig figcaption { margin-top: 0.3rem; font-size: 13.5px; color: var(--dim); }
.fig .guide { fill: none; stroke: var(--dim); stroke-width: 1.2; stroke-dasharray: 4 4; }
.fig .ray { stroke: var(--muted); stroke-width: 1.3; }
.fig .bar { fill: var(--accent-dim); stroke: var(--accent); stroke-width: 1.5; }
.fig .bar.child { fill: var(--warn-dim); stroke: var(--warn); }
.fig .dot { fill: var(--accent); }
.fig .hot { fill: #e07a6a; }
.fig text { fill: var(--muted); font-family: var(--mono); font-size: 11px; }

.hint {
  font-size: 0.92rem;
  color: var(--dim);
  margin: 0.85rem 0 1.15rem;
}

/* ── Code panel ── */
.code-panel {
  position: relative;
  background: var(--bg-code);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  margin: 1.15rem 0 1.35rem;
}

.code-bar {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 0.75rem;
  padding: 0.45rem 0.7rem 0.45rem 0.9rem;
  border-bottom: 1px solid var(--border);
  background: var(--bg-elev);
}

.legend {
  display: flex;
  gap: 0.9rem;
  font-size: 11.5px;
  color: var(--dim);
}

.legend span { display: inline-flex; align-items: center; gap: 0.38rem; }

.swatch {
  width: 0.7rem;
  height: 0.7rem;
  border-radius: 2px;
  display: inline-block;
}

.swatch.new {
  background: var(--ok-dim);
  box-shadow: inset 0 0 0 1px var(--ok-line);
}

.swatch.old {
  background: #1c1f26;
  box-shadow: inset 0 0 0 1px #3a414c;
}

.code-actions { display: flex; gap: 0.4rem; }

.copy-btn, .ghost-btn {
  font: inherit;
  font-size: 12px;
  font-weight: 500;
  cursor: pointer;
  border-radius: 5px;
  padding: 0.28rem 0.6rem;
}

.copy-btn {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--muted);
}

.copy-btn:hover { color: var(--text); border-color: var(--accent-line); }

.copy-btn.ok {
  color: var(--ok);
  border-color: rgba(134, 196, 154, 0.4);
}

.ghost-btn {
  background: transparent;
  border: 1px solid transparent;
  color: var(--dim);
}

.ghost-btn:hover { color: var(--text); }

pre.code {
  margin: 0;
  padding: 0.7rem 0 0.85rem;
  overflow-x: auto;
  font-family: var(--mono);
  font-size: var(--fs-code);
  line-height: 1.62;
  tab-size: 4;
}

.line {
  display: grid;
  grid-template-columns: 2.6rem 1fr;
  min-height: 1.62em;
}

.line .ln {
  text-align: right;
  padding-right: 0.85rem;
  color: #4e5662;
  user-select: none;
  font-size: 11.5px;
}

.line .src {
  padding: 0 1rem 0 0.85rem;
  white-space: pre;
}

.line.old .src { color: var(--old-fg); }

.line.new {
  background: var(--ok-dim);
  box-shadow: inset 3px 0 0 var(--ok-line);
}

.line.new .src { color: var(--new-fg); }
.line.new .ln { color: #8fbf9a; }

.line.focus {
  background: var(--accent-dim);
  box-shadow: inset 3px 0 0 var(--accent);
}

.line.focus .src { color: var(--text); }
.line.focus .ln { color: var(--accent); }

/* syntax, applied on tokens inside .src */
.tok-kw { color: #8eb4d4; }
.tok-str { color: #c9a87c; }
.tok-cmt { color: #6a7380; font-style: italic; }
.tok-num { color: #c48a7a; }
.tok-dec { color: #7ec8b4; }
.tok-api { color: #b7a8d4; }
.line.old .tok-kw,
.line.old .tok-str,
.line.old .tok-num,
.line.old .tok-dec,
.line.old .tok-api { opacity: 0.72; }

/* ── Try also ── */
.try {
  background: var(--warn-dim);
  border: 1px solid rgba(196, 165, 116, 0.22);
  border-radius: var(--radius);
  padding: 0.95rem 1.05rem 1.05rem;
  margin-bottom: 1.5rem;
}

.try h2 {
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--warn);
  margin-bottom: 0.55rem;
}

.try > p {
  color: var(--muted);
  font-size: 0.95rem;
  margin-bottom: 0.75rem;
}


/* ── Para entender melhor (concept box) ── */
.dive {
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent-line);
  border-radius: var(--radius);
  padding: 0.95rem 1.05rem 1.05rem;
  margin-bottom: 1.5rem;
}

.dive h2 {
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.3rem;
}

.dive h3 {
  font-size: 1.05rem;
  margin-bottom: 0.5rem;
}

.dive-body p {
  font-size: 0.95rem;
  margin-bottom: 0.6rem;
}

.alt {
  margin-top: 0.7rem;
}

.alt p {
  font-size: 0.9rem;
  color: var(--muted);
  margin-bottom: 0.35rem;
}

.alt .code-panel { margin: 0; }

.alt .code-bar {
  background: transparent;
  padding: 0.3rem 0.65rem;
}

/* ── Nav ── */
.step-nav {
  display: flex;
  justify-content: space-between;
  gap: 0.75rem;
  margin-top: 1.75rem;
  padding-top: 1.15rem;
  border-top: 1px solid var(--border);
}

.nav-btn {
  font: inherit;
  font-size: 0.92rem;
  font-weight: 500;
  padding: 0.5rem 0.9rem;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: var(--bg-elev);
  color: var(--text);
  cursor: pointer;
}

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

.nav-btn:disabled {
  opacity: 0.35;
  cursor: default;
  color: var(--dim);
}

.nav-btn:disabled:hover { border-color: var(--border); color: var(--dim); }

.nav-btn.primary {
  background: var(--accent-dim);
  border-color: var(--accent-line);
  color: var(--accent);
}

.closing {
  margin-top: 1.25rem;
  padding: 0.9rem 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--bg-elev);
  color: var(--muted);
  font-size: 0.95rem;
}

.closing pre {
  margin-top: 0.5rem;
  font-family: var(--mono);
  font-size: 13px;
  color: var(--text);
}

.recap {
  margin-top: 1.25rem;
  padding: 0.9rem 1rem 1rem;
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent-line);
  border-radius: var(--radius);
  background: var(--bg-elev);
  font-size: 0.95rem;
}

.recap h2 {
  margin: 0 0 0.5rem;
  font-size: 0.8rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--accent);
}

.recap ul {
  margin: 0 0 0.6rem;
  padding-left: 1.2rem;
}

.recap li { margin: 0.25rem 0; }

.recap p {
  margin: 0.4rem 0 0;
  color: var(--muted);
}

.menu-btn {
  display: none;
  position: fixed;
  top: 0.75rem;
  left: 0.75rem;
  z-index: 30;
  background: var(--bg-elev);
  border: 1px solid var(--border);
  color: var(--text);
  border-radius: 6px;
  padding: 0.4rem 0.65rem;
  font: inherit;
  font-size: 13px;
  cursor: pointer;
}

/* ── Index ── */
.index-wrap {
  max-width: 40rem;
  margin: 0 auto;
  padding: 4rem 1.5rem 5rem;
}

.index-wrap .eyebrow {
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.6rem;
}

.index-wrap h1 {
  font-size: 2rem;
  font-weight: 700;
  letter-spacing: -0.04em;
  margin-bottom: 0.55rem;
}

.index-wrap .lede {
  color: var(--muted);
  margin-bottom: 2rem;
}

/* A second list on the index (the appendices), after the tutorials. */
.index-wrap .index-section {
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  margin: 3.5rem 0 0.45rem;
}

.card {
  display: block;
  background: var(--bg-elev);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1.15rem 1.25rem 1.2rem;
  color: inherit;
  text-decoration: none;
}

.card + .card { margin-top: 0.75rem; }

.card:hover {
  border-color: var(--accent-line);
  text-decoration: none;
}

/* A tutorial that has its number but no page yet (a <div class="card">). */
div.card { border-style: dashed; opacity: 0.7; }
div.card:hover { border-color: var(--border); }

.card .num {
  font-family: var(--mono);
  font-size: 12px;
  color: var(--accent);
  margin-bottom: 0.25rem;
}

.card h2 {
  font-size: 1.15rem;
  font-weight: 600;
  letter-spacing: -0.02em;
  margin-bottom: 0.3rem;
}

.card p { color: var(--muted); font-size: 0.95rem; }

@media (max-width: 860px) {
  .page { grid-template-columns: 1fr; }
  .sidebar {
    position: fixed;
    z-index: 20;
    transform: translateX(-105%);
    transition: transform 0.18s ease;
    width: min(80vw, 300px);
  }
  body.nav-open .sidebar { transform: none; }
  .menu-btn { display: block; }
  main { padding: 3.6rem 1.1rem 5rem; }
}