/* ai.bystruev.com — trilingual static landing. System stacks only, no webfonts. */
:root {
  --paper: #ffffff;
  --ink: #1a1d21;
  --ink-soft: #3d434b;
  --muted: #6b7280;
  --line: #e3e1da;
  --rail: #0f766e;
  --rail-dark: #0b4f4a;
  --signal: #c2410c;
  --signal-soft: #fdf1e7;
  --mint: #eef7f4;
  --amber-soft: #fbf6e9;
  --mono: ui-monospace, "SF Mono", "Cascadia Mono", Menlo, Consolas, monospace;
  --serif: Charter, "Bitstream Charter", "Sitka Text", Cambria, Georgia, serif;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
  --max: 1080px;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--sans);
  color: var(--ink);
  background: var(--paper);
  line-height: 1.6;
}
.wrap { max-width: var(--max); margin: 0 auto; padding: 0 24px; }

/* ---------- header ---------- */
.site-header {
  border-bottom: 1px solid var(--line);
  position: sticky; top: 0; background: rgba(255,255,255,.96); z-index: 50;
}
.site-header .wrap {
  display: flex; align-items: center; gap: 28px;
  min-height: 62px;
}
.brand { font-family: var(--mono); font-weight: 700; font-size: 17px; text-decoration: none; color: var(--ink); white-space: nowrap; }
.brand b { color: var(--rail); }
nav.main { display: flex; gap: 20px; margin-left: auto; }
nav.main a { color: var(--ink-soft); text-decoration: none; font-size: 14.5px; }
nav.main a:hover { color: var(--rail-dark); text-decoration: underline; }
.lang { display: flex; gap: 0; border: 1px solid var(--line); border-radius: 999px; overflow: hidden; font-size: 13px; }
.lang a, .lang span {
  padding: 5px 11px; text-decoration: none; color: var(--muted);
  font-family: var(--mono);
}
.lang span { background: var(--ink); color: #fff; }
.lang a:hover { background: var(--mint); color: var(--ink); }
@media (max-width: 760px) { nav.main { display: none; } }

/* ---------- hero ---------- */
.hero { padding: 72px 0 40px; }
.hero-grid { display: grid; grid-template-columns: 1.05fr .95fr; gap: 48px; align-items: start; }
@media (max-width: 860px) { .hero-grid { grid-template-columns: 1fr; } }
.hero h1 {
  font-family: var(--serif); font-weight: 700;
  font-size: clamp(34px, 4.6vw, 52px); line-height: 1.12;
  margin: 0 0 18px; letter-spacing: -0.01em;
}
.hero h1 em { font-style: italic; color: var(--rail-dark); }
.lede { font-size: 18px; color: var(--ink-soft); margin: 0 0 26px; max-width: 34em; }
.cta-row { display: flex; gap: 12px; flex-wrap: wrap; margin-bottom: 30px; }
.btn {
  display: inline-block; padding: 12px 22px; border-radius: 8px;
  text-decoration: none; font-weight: 600; font-size: 15.5px;
}
.btn-solid { background: var(--rail); color: #fff; }
.btn-solid:hover { background: var(--rail-dark); }
.btn-ghost { border: 1.5px solid var(--ink); color: var(--ink); }
.btn-ghost:hover { background: var(--ink); color: #fff; }
.stats { display: flex; gap: 26px; flex-wrap: wrap; border-top: 1px solid var(--line); padding-top: 20px; }
.stat { min-width: 130px; }
.stat .n { font-family: var(--mono); font-weight: 700; font-size: 22px; color: var(--ink); }
.stat .n i { font-style: normal; color: var(--signal); }
.stat .d { font-size: 13px; color: var(--muted); max-width: 170px; }

/* rail schematic */
.railcard {
  border: 1px solid var(--line); border-radius: 12px;
  background: #101315; color: #d7dde3;
  padding: 22px 22px 18px;
  font-family: var(--mono); font-size: 13px;
}
.railcard .cap { color: #8b949e; font-size: 12px; margin-bottom: 12px; }
.station { display: flex; gap: 10px; align-items: flex-start; padding: 7px 0; }
.station .dot {
  flex: 0 0 auto; width: 12px; height: 12px; border-radius: 50%;
  background: #2dd4bf; margin-top: 4px;
}
.station.human .dot { background: #fb923c; }
.station .who { color: #7dd3fc; }
.station.human .who { color: #fdba74; }
.station .what { color: #d7dde3; }
.station .note { color: #8b949e; font-size: 12px; display: block; }
.rail-line { width: 2px; background: #2b333b; margin-left: 5px; height: 14px; }
.railcard .loop {
  margin-top: 12px; border-top: 1px dashed #2b333b; padding-top: 12px;
  color: #8b949e; font-size: 12.5px;
}
.railcard .loop b { color: #2dd4bf; font-weight: 600; }

/* ---------- sections ---------- */
section.block { padding: 56px 0; border-top: 1px solid var(--line); }
.kicker {
  font-family: var(--mono); font-size: 13px; color: var(--signal);
  margin: 0 0 10px;
}
h2 {
  font-family: var(--serif); font-size: clamp(26px, 3.2vw, 36px);
  line-height: 1.2; margin: 0 0 14px; letter-spacing: -0.01em;
}
.sub { color: var(--ink-soft); font-size: 17px; max-width: 44em; margin: 0 0 28px; }
.math {
  background: var(--amber-soft); border: 1px solid #eadfc2; border-radius: 10px;
  padding: 18px 22px; font-size: 16px; max-width: 46em; margin: 0 0 28px;
}
.math code { font-family: var(--mono); background: #fff; padding: 1px 7px; border-radius: 5px; border: 1px solid var(--line); }
.cols2 { display: grid; grid-template-columns: 1fr 1fr; gap: 22px; }
@media (max-width: 760px) { .cols2 { grid-template-columns: 1fr; } }
.panel { border: 1px solid var(--line); border-radius: 10px; padding: 22px 24px; }
.panel h3 { margin: 0 0 10px; font-size: 18px; }
.panel.no { background: #fef6f3; border-color: #f0d9cd; }
.panel.yes { background: var(--mint); border-color: #c8e4da; }
ul.tight { margin: 8px 0 0; padding-left: 20px; }
ul.tight li { margin: 7px 0; }
ul.tight li::marker { color: var(--rail); }
.panel.no ul.tight li::marker { color: var(--signal); }

/* steps */
.steps { list-style: none; margin: 0; padding: 0; counter-reset: s; }
.steps li {
  counter-increment: s; display: grid; grid-template-columns: 52px 1fr; gap: 16px;
  padding: 16px 0; border-top: 1px solid var(--line);
}
.steps li::before {
  content: counter(s, decimal-leading-zero);
  font-family: var(--mono); font-weight: 700; font-size: 20px; color: var(--rail);
}
.steps li h3 { margin: 0 0 4px; font-size: 17.5px; }
.steps li p { margin: 0; color: var(--ink-soft); }
.steps li p code, p code, li code {
  font-family: var(--mono); font-size: .86em; background: #f2f1ec;
  padding: 1px 6px; border-radius: 5px; border: 1px solid var(--line);
}

/* industries */
.industry { border: 1px solid var(--line); border-radius: 12px; padding: 28px; margin: 0 0 22px; }
.industry:last-child { margin-bottom: 0; }
.industry h3 { font-family: var(--serif); font-size: 23px; margin: 0 0 6px; }
.industry .tag {
  display: inline-block; font-family: var(--mono); font-size: 12.5px;
  background: var(--ink); color: #fff; border-radius: 999px; padding: 2px 12px; margin-bottom: 12px;
}
.flow {
  font-family: var(--mono); font-size: 13.5px; background: #101315; color: #d7dde3;
  border-radius: 8px; padding: 14px 18px; margin: 14px 0; overflow-x: auto; white-space: nowrap;
}
.flow b { color: #2dd4bf; font-weight: 600; }
.flow .ok { color: #fdba74; }
.result { border-left: 3px solid var(--rail); padding-left: 14px; color: var(--ink-soft); margin: 12px 0 0; }

/* stack + faq + contact */
.stack { display: flex; flex-wrap: wrap; gap: 10px; margin: 18px 0 0; }
.stack span {
  font-family: var(--mono); font-size: 13px; border: 1px solid var(--line);
  border-radius: 999px; padding: 5px 14px; background: #f7f6f2;
}
details { border: 1px solid var(--line); border-radius: 8px; padding: 14px 18px; margin: 0 0 10px; }
summary { cursor: pointer; font-weight: 600; font-size: 16px; }
details p { margin: 10px 0 0; color: var(--ink-soft); }
.contact {
  background: var(--rail-dark); color: #eaf4f1; border-radius: 14px;
  padding: 44px 40px; margin-top: 8px;
}
.contact h2 { color: #fff; }
.contact p { color: #c4d8d2; max-width: 40em; }
.contact .btn-solid { background: #fff; color: var(--rail-dark); }
.contact .btn-solid:hover { background: var(--mint); }
.contact a.mail { color: #fff; font-family: var(--mono); }
footer { border-top: 1px solid var(--line); padding: 26px 0 40px; color: var(--muted); font-size: 13.5px; }
footer .wrap { display: flex; gap: 18px; flex-wrap: wrap; align-items: center; }
footer a { color: var(--muted); }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }