:root {
  --mono: "IBM Plex Mono", ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  --sans: "IBM Plex Sans", system-ui, Arial, sans-serif;
  --display: "IBM Plex Sans", system-ui, Arial, sans-serif;
  --t: .2s ease;

  /* light */
  --page: #ffffff;
  --ink: #1c2024;
  --body: #5d6c7b;
  --muted: #8b98a5;
  --rule: #c9d1d8;
  --rule-soft: #e4e7ea;
  --surface: #eef0f2;
  --code-bg: #eaecef;
  --code-ink: #2b4a2a;
  --tty-bg: #1b1f24;
  --tty-rule: #2c333b;
  --accent: #15b757;
  --accent-hot: #fb4a00;
  --link: #1b370e;
  --ink-alt: #3a668f;
  --hero-a: #f6f7f8;
  --hero-b: #fdfdfd;
  --hero-c: #eceef0;
  --band: #1b370e;
  --band-ink: #b9c8b2;
  --band-ink-soft: #91a48b;
  --band-link: #dcebd6;
  --sx-k: #0d7a3c;
  --sx-n: #2f5a80;
  --sx-v: #8a5a12;
  --sx-c: #7c8b99;
  --sx-op: #c23c06;
  color-scheme: light;
}

/* dark: system preference, unless the reader has explicitly chosen light */
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --page: #14171a;
    --ink: #e6eaee;
    --body: #9fadba;
    --muted: #74828f;
    --rule: #2c333b;
    --rule-soft: #232a30;
    --surface: #1b1f24;
    --code-bg: #1b1f24;
    --code-ink: #8fd6a8;
    --tty-bg: #0b0e11;
    --tty-rule: #363f49;
    --accent: #2fd06f;
    --accent-hot: #ff7a4d;
    --link: #7fdca0;
    --ink-alt: #7fb2e5;
    --hero-a: #171b1f;
    --hero-b: #14171a;
    --hero-c: #101316;
    --band: #0f1d0a;
    --band-ink: #a9bda2;
    --band-ink-soft: #8b9d85;
    --band-link: #cfe6c7;
    --sx-k: #4ec97a;
    --sx-n: #7fb2e5;
    --sx-v: #e3b341;
    --sx-c: #6b7885;
    --sx-op: #f2704f;
    color-scheme: dark;
  }
}

/* dark: explicit choice, so the toggle wins in both directions */
:root[data-theme="dark"] {
  --page: #14171a;
  --ink: #e6eaee;
  --body: #9fadba;
  --muted: #74828f;
  --rule: #2c333b;
  --rule-soft: #232a30;
  --surface: #1b1f24;
  --code-bg: #1b1f24;
  --code-ink: #8fd6a8;
  --tty-bg: #0b0e11;
  --tty-rule: #363f49;
  --accent: #2fd06f;
  --accent-hot: #ff7a4d;
  --link: #7fdca0;
  --ink-alt: #7fb2e5;
  --hero-a: #171b1f;
  --hero-b: #14171a;
  --hero-c: #101316;
  --band: #0f1d0a;
  --band-ink: #a9bda2;
  --band-ink-soft: #8b9d85;
  --band-link: #cfe6c7;
  --sx-k: #4ec97a;
  --sx-n: #7fb2e5;
  --sx-v: #e3b341;
  --sx-c: #6b7885;
  --sx-op: #f2704f;
  color-scheme: dark;
}
* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 5rem; -webkit-text-size-adjust: 100%; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation: none !important; transition: none !important; }
}
body {
  background: var(--page);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 1rem;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}
::selection { background: var(--accent); color: var(--page); }
a { color: var(--link); text-decoration: none; text-underline-offset: 3px; }
a:hover, a:focus-visible { text-decoration: underline; text-decoration-color: var(--accent); }
:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
code, pre, kbd { font-family: var(--mono); }
code {
  background: var(--surface); border: 1px solid var(--rule-soft); border-radius: 2px;
  padding: 0.1em 0.35em; font-size: 0.85em; color: var(--code-ink);
}
pre {
  background: var(--code-bg);
  color: var(--ink);
  border: 1px solid var(--rule);
  border-radius: 2px;
  padding: 1.25rem 1.4rem;
  overflow-x: auto;
  font-size: 0.82rem;
  line-height: 1.7;
}
pre code { background: none; border: none; padding: 0; font-size: inherit; color: inherit; }
kbd {
  background: var(--page); color: var(--ink);
  border: 1px solid var(--rule); border-bottom-width: 2px; border-radius: 2px;
  padding: 0.06em 0.4em; font-size: 0.78em; white-space: nowrap;
}

/* LP + code syntax colours (on the pale code panel) */
.k  { color: var(--sx-k); font-weight: 600; }
.n  { color: var(--sx-n); }
.v  { color: var(--sx-v); }
.c  { color: var(--sx-c); font-style: italic; }
.op { color: var(--sx-op); }
.g  { color: var(--sx-k); }
.r  { color: var(--sx-op); }
.y  { color: var(--sx-v); }

/* ---- page frame: hairline rules down both edges of every band ---- */
.wrap {
  max-width: 78rem; margin: 0 auto; padding: 0 3.5rem;
  border-left: 1px solid var(--rule); border-right: 1px solid var(--rule);
}
@media (max-width: 760px) { .wrap { padding: 0 1.25rem; } }

/* ---- nav ---- */
nav {
  position: sticky; top: 0; z-index: 20;
  background: color-mix(in srgb, var(--page) 86%, transparent);
  backdrop-filter: saturate(180%) blur(10px);
  border-bottom: 1px solid var(--rule);
}
nav .row {
  max-width: 78rem; margin: 0 auto; padding: 1.05rem 3.5rem;
  border-left: 1px solid var(--rule); border-right: 1px solid var(--rule);
  display: flex; gap: 1.75rem; align-items: center;
}
nav .links { display: flex; gap: 1.75rem; align-items: center; min-width: 0; }
@media (max-width: 760px) { nav .row { padding: 0.9rem 1.25rem; gap: 1rem; } }
nav .brand {
  font-family: var(--mono); font-size: 0.9rem; font-weight: 600;
  color: var(--ink); margin-right: auto; letter-spacing: -0.02em;
}
nav a { color: var(--ink); font-size: 0.9rem; transition: color var(--t); }
nav a:hover { color: var(--accent-hot); text-decoration: none; }

/* ---- hero ---- */
header.hero {
  background-image: linear-gradient(var(--hero-a), var(--hero-b) 20% 80%, var(--hero-c));
  border-bottom: 1px solid var(--rule);
  padding: 6.5rem 0 5rem;
}
.eyebrow {
  font-family: var(--mono); font-size: 0.72rem; letter-spacing: 0.14em;
  text-transform: uppercase; color: var(--muted); margin-bottom: 2rem;
}
h1 {
  font-family: var(--display);
  font-size: clamp(2rem, 5.2vw, 4rem);
  line-height: 1.08;
  font-weight: 400;
  letter-spacing: -0.018em;
  color: var(--muted);
}
h1 .line2 { display: block; color: var(--ink); font-weight: 500; }
.hero p.sub {
  margin: 1.5rem 0 0; color: var(--body);
  font-size: 1.0625rem; max-width: 33rem;
}
.hero p.sub a { color: var(--link); text-decoration: underline; text-decoration-color: var(--rule); }
.badges {
  display: flex; gap: 0; flex-wrap: wrap;
  margin: 2.25rem 0 0; font-size: 0.73rem; width: fit-content; max-width: 100%;
  border: 1px solid var(--rule); background: var(--page);
}
.badges span {
  padding: 0.45rem 0.85rem; color: var(--body);
  border-right: 1px solid var(--rule);
}
.badges span:last-child { border-right: none; }
.badges span b { color: var(--ink); font-weight: 600; font-family: var(--mono); font-size: 0.95em; }
.cta { margin-top: 2.25rem; display: flex; gap: 0.75rem; flex-wrap: wrap; }

/* square outline button with its own arrow tile */
.cta a {
  position: relative; display: inline-flex; align-items: center; gap: 1.5rem;
  font-size: 0.9rem; font-weight: 600; color: var(--link);
  border: 1px solid var(--rule); background: var(--page);
  padding: 0 0 0 1.25rem; overflow: hidden;
  transition: background var(--t), border-color var(--t), color var(--t);
}
.cta a::after {
  content: "↗"; display: flex; align-items: center; justify-content: center;
  width: 3rem; height: 3rem; flex: none;
  border-left: 1px solid var(--rule); color: var(--accent);
  font-size: 1.05rem; font-weight: 400;
  transition: border-color var(--t), color var(--t), background var(--t);
}
.cta a:hover { background: var(--surface); text-decoration: none; }
.cta a.primary { background: var(--accent); border-color: var(--accent); color: #06240f; }
.cta a.primary::after { border-left-color: #06240f; color: #06240f; }
.cta a.primary:hover { filter: brightness(.92); }
.hero pre { max-width: 46rem; margin: 3.5rem 0 0; }

/* ---- sections ---- */
body { counter-reset: sec; }
section { padding: 5.5rem 0; border-bottom: 1px solid var(--rule); }
.sec-label {
  counter-increment: sec;
  font-family: var(--mono); font-size: 0.72rem; letter-spacing: 0.14em;
  text-transform: uppercase; color: var(--muted); margin-bottom: 1.25rem;
  display: flex; align-items: baseline; gap: 0.9rem;
}
.sec-label::before {
  content: counter(sec, decimal-leading-zero); color: var(--accent); font-weight: 600; letter-spacing: 0.04em;
}
h2 {
  font-family: var(--display);
  font-size: clamp(1.75rem, 3.4vw, 2.5rem);
  font-weight: 400; letter-spacing: -0.018em; line-height: 1.15;
  color: var(--ink); margin-bottom: 1rem; max-width: 30rem;
}
h2 code { font-size: 0.68em; background: var(--surface); border-color: var(--rule-soft); }
h3 {
  font-family: var(--display); font-size: 1.2rem; margin: 3rem 0 0.9rem;
  color: var(--ink); font-weight: 600; letter-spacing: -0.01em;
  padding-top: 0.9rem; border-top: 1px solid var(--rule-soft);
}
section > .wrap > p, section p.lead { color: var(--body); max-width: 44rem; }
section p.lead { font-size: 1.05rem; }
p + pre, p + table, ul + pre, p + .tablewrap { margin-top: 1.1rem; }
pre + p, table + p, pre + h3, .tablewrap + p { margin-top: 1.4rem; }

/* cards — flat, hairline-bordered, sharp */
.cards {
  display: grid; grid-template-columns: 1fr 1fr; gap: 0;
  margin-top: 2.5rem; border: 1px solid var(--rule);
}
.card {
  background: var(--page); padding: 2rem 2rem 2.25rem;
  border-right: 1px solid var(--rule); border-bottom: 1px solid var(--rule);
  transition: background var(--t);
}
.card:nth-child(2n) { border-right: none; }
.card:nth-last-child(-n+2) { border-bottom: none; }
.card:hover { background: var(--surface); }
.card h4 { font-family: var(--mono); font-size: 0.9rem; margin-bottom: 0.6rem; font-weight: 600; }
.card h4 a { color: var(--ink); }
.card h4 a:hover { color: var(--ink-alt); }
.card p { font-size: 0.92rem; color: var(--body); }
@media (max-width: 640px) {
  .cards { grid-template-columns: 1fr; }
  .card { border-right: none; }
  .card:nth-last-child(-n+2) { border-bottom: 1px solid var(--rule); }
  .card:last-child { border-bottom: none; }
}

/* constraint list — capabilities rendered as LP constraints */
ul.constraints { list-style: none; margin-top: 2.5rem; border-top: 1px solid var(--rule); }
ul.constraints li {
  padding: 1.1rem 0; border-bottom: 1px solid var(--rule-soft);
  display: grid; grid-template-columns: 13rem 1fr; gap: 2rem;
}
ul.constraints .cname { font-family: var(--mono); font-size: 0.8rem; color: var(--ink-alt); font-weight: 500; }
ul.constraints .cname::after { content: ":"; color: var(--muted); }
ul.constraints .cbody { font-size: 0.95rem; color: var(--body); }
@media (max-width: 700px) { ul.constraints li { grid-template-columns: 1fr; gap: 0.3rem; } }

/* tables */
.tablewrap { overflow-x: auto; border: 1px solid var(--rule); margin-top: 1.25rem; }
table { border-collapse: collapse; width: 100%; font-size: 0.88rem; }
th, td { text-align: left; padding: 0.75rem 1.1rem; border-bottom: 1px solid var(--rule-soft); vertical-align: top; }
tr:last-child td { border-bottom: none; }
th {
  font-family: var(--mono); font-size: 0.68rem; text-transform: uppercase;
  letter-spacing: 0.12em; color: var(--muted); font-weight: 600;
  background: var(--surface); border-bottom-color: var(--rule);
}
td { color: var(--body); }
td:first-child { font-family: var(--mono); font-size: 0.8rem; color: var(--ink); }

img.demo, video.demo {
  max-width: 100%; height: auto; display: block;
  border: 1px solid var(--rule); margin-top: 2.5rem; background: #14171a;
}

/* footer: the one dark band on the page */
footer {
  background: var(--band); color: var(--band-ink);
  padding: 5rem 0 5.5rem;
}
footer .wrap { border-color: rgba(255,255,255,.14); }
footer .end {
  font-family: var(--display); font-weight: 400; letter-spacing: -0.018em;
  color: #ffffff; font-size: clamp(1.75rem, 3.4vw, 2.5rem); line-height: 1.1;
}
footer p { color: var(--band-ink-soft); font-size: 0.88rem; margin-top: 1.25rem; }
footer a { color: var(--band-link); text-decoration: underline; text-decoration-color: rgba(220,235,214,.35); }
footer a:hover { color: var(--accent); }

/* ---- deep-dive page additions (tui.html) ---- */

/* consecutive body paragraphs need a gap; the base rules only spaced
   paragraphs against code blocks and tables */
section p + p, .note + p { margin-top: 1rem; }

/* sub-navigation for a long single-topic page */
.subnav {
  display: flex; flex-wrap: wrap; gap: 0;
  border: 1px solid var(--rule); margin-top: 2.5rem; background: var(--page);
  font-size: 0.8rem; font-family: var(--mono);
}
.subnav a {
  padding: 0.6rem 1.1rem; color: var(--body);
  border-right: 1px solid var(--rule-soft);
}
.subnav a:last-child { border-right: none; }
.subnav a:hover { background: var(--surface); color: var(--ink); text-decoration: none; }

/* key-binding tables: tighter, monospace first column already handled by td:first-child */
table.keys td:first-child { white-space: nowrap; }
table.keys kbd { margin-right: 0.15rem; }

/* a terminal-style panel for showing real TUI output */
pre.tty {
  background: var(--tty-bg); color: #d6dbe1; border-color: var(--tty-rule);
  font-size: 0.76rem; line-height: 1.55;
}
pre.tty .dim { color: #8a95a1; }
pre.tty .ok { color: #4ec97a; }
pre.tty .warn { color: #e3b341; }
pre.tty .bad { color: #f2704f; }
pre.tty .hdr { color: #7fb2e5; font-weight: 600; }

/* callout for the "why this matters" asides */
.note {
  border: 1px solid var(--rule); background: var(--surface);
  padding: 1rem 1.25rem; margin-top: 1.5rem; font-size: 0.92rem; color: var(--body);
  max-width: 44rem;
}
.note b { color: var(--ink); font-weight: 600; }

/* back-link at the top of a sub-page */
.backlink {
  font-family: var(--mono); font-size: 0.78rem; color: var(--muted);
  display: inline-block; margin-bottom: 1.5rem;
}
.backlink:hover { color: var(--accent-hot); text-decoration: none; }

/* three-up card grid for the diagnostics signals */
.cards.three { grid-template-columns: 1fr 1fr 1fr; }
.cards.three .card:nth-child(2n) { border-right: 1px solid var(--rule); }
.cards.three .card:nth-child(3n) { border-right: none; }
.cards.three .card:nth-last-child(-n+3) { border-bottom: none; }
@media (max-width: 860px) {
  .cards.three { grid-template-columns: 1fr; }
  .cards.three .card, .cards.three .card:nth-child(2n) { border-right: none; }
  .cards.three .card { border-bottom: 1px solid var(--rule); }
  .cards.three .card:last-child { border-bottom: none; }
}

/* ---- theme toggle: sits at the end of the nav row ---- */
.theme-toggle {
  flex: none; font: inherit; font-family: var(--mono); font-size: 0.78rem;
  line-height: 1; color: var(--body); background: none;
  border: 1px solid var(--rule); padding: 0.42rem 0.6rem; cursor: pointer;
  transition: color var(--t), border-color var(--t);
}
.theme-toggle:hover { color: var(--ink); border-color: var(--muted); }

/* ---- narrow screens: one scrollable nav row rather than a wrapped block ---- */
@media (max-width: 760px) {
  nav .row { gap: 0.85rem; }
  nav .brand { margin-right: 0; }
  nav .links { flex: 1; gap: 1.1rem; overflow-x: auto; scrollbar-width: none; }
  nav .links::-webkit-scrollbar { display: none; }
  nav a, .theme-toggle { flex: none; }
}

/* ---- wide screens: the hero runs two-up, copy beside the example ---- */
@media (min-width: 62rem) {
  header.hero { padding: 5rem 0 4.5rem; }
  .hero .wrap {
    display: grid; grid-template-columns: minmax(0, 30rem) minmax(0, 1fr);
    gap: 4rem; align-items: center;
  }
  /* the column is 30rem, not the full page: the display size has to come down with it */
  .hero h1 { font-size: clamp(2rem, 3.2vw, 2.9rem); }
  .hero .eyebrow { margin-bottom: 1.5rem; }
  .hero pre { margin: 0; max-width: none; }
  .hero img.demo, .hero video.demo { margin-top: 0; }
}