:root {
  --bg: #fafaf9;
  --bg-alt: #f2f2ef;
  --surface: #ffffff;
  --ink: #12151c;
  --muted: #5d6472;
  --line: #e2e2dd;
  --brand: #5b6cff;
  --brand-ink: #ffffff;
  --brand-soft: #eceeff;
  --allow: #0f9d58;
  --allow-bg: #e3f5ea;
  --esc: #b26a00;
  --esc-bg: #fdf0d8;
  --deny: #d03a3a;
  --deny-bg: #fbe6e6;
  --term-bg: #0d1117;
  --term-ink: #d7dde8;
  --term-dim: #7d8696;
  --shadow: 0 1px 2px rgba(18, 21, 28, .06), 0 12px 32px rgba(18, 21, 28, .08);
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --r: 14px;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0b0e14;
    --bg-alt: #10141c;
    --surface: #141922;
    --ink: #e9ecf2;
    --muted: #98a1b2;
    --line: #232a37;
    --brand: #7b88ff;
    --brand-soft: #1c2140;
    --allow: #3ddc97;
    --allow-bg: #11302280;
    --esc: #f3b54a;
    --esc-bg: #3a2a0f80;
    --deny: #ff6b6b;
    --deny-bg: #3a151580;
    --term-bg: #080b10;
    --shadow: 0 1px 2px rgba(0, 0, 0, .4), 0 12px 32px rgba(0, 0, 0, .35);
  }
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 76px; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font: 16px/1.6 var(--sans);
  -webkit-font-smoothing: antialiased;
}
img, svg { max-width: 100%; }
a { color: inherit; }
code { font-family: var(--mono); font-size: .88em; background: var(--brand-soft); padding: .1em .4em; border-radius: 6px; }
b { font-weight: 650; }

/* language toggle */
html[lang="vi"] .en { display: none !important; }
html[lang="en"] .vi { display: none !important; }

.wrap { width: min(1140px, 100% - 32px); margin-inline: auto; }
.narrow { width: min(760px, 100% - 32px); margin-inline: auto; }
.center { text-align: center; }

/* nav */
.nav {
  position: sticky; top: 0; z-index: 20;
  background: color-mix(in srgb, var(--bg) 85%, transparent);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--line);
}
.nav-in { display: flex; align-items: center; gap: 24px; height: 62px; }
.brand { display: inline-flex; align-items: center; gap: 9px; font-weight: 750; font-size: 19px; letter-spacing: .02em; text-decoration: none; }
.links { display: flex; gap: 22px; margin-left: 12px; flex: 1; }
.links a { color: var(--muted); text-decoration: none; font-size: 14.5px; }
.links a:hover { color: var(--ink); }
.nav-r { display: flex; align-items: center; gap: 12px; margin-left: auto; }
.lang { display: inline-flex; border: 1px solid var(--line); border-radius: 999px; padding: 2px; }
.lang button {
  border: 0; background: none; color: var(--muted); font: 600 12px var(--sans);
  padding: 5px 10px; border-radius: 999px; cursor: pointer;
}
.lang button[aria-pressed="true"] { background: var(--ink); color: var(--bg); }

.btn {
  display: inline-flex; align-items: center; justify-content: center;
  background: var(--brand); color: var(--brand-ink);
  border: 1px solid transparent; border-radius: 10px;
  padding: 12px 20px; font: 600 15px var(--sans); text-decoration: none; cursor: pointer;
  transition: transform .15s, box-shadow .15s, filter .15s;
}
.btn:hover { filter: brightness(1.08); transform: translateY(-1px); box-shadow: 0 8px 20px color-mix(in srgb, var(--brand) 35%, transparent); }
.btn-sm { padding: 8px 14px; font-size: 14px; }
.btn-ghost { background: transparent; color: var(--ink); border-color: var(--line); }
.btn-ghost:hover { box-shadow: none; background: var(--surface); }
:focus-visible { outline: 2px solid var(--brand); outline-offset: 2px; border-radius: 6px; }

/* hero */
.hero {
  padding: 72px 0 80px;
  background:
    radial-gradient(900px 420px at 85% -10%, color-mix(in srgb, var(--brand) 16%, transparent), transparent 70%),
    linear-gradient(var(--line) 1px, transparent 1px) 0 0 / 100% 56px,
    var(--bg);
}
.hero-grid { display: grid; grid-template-columns: 1.05fr .95fr; gap: 48px; align-items: center; }
.eyebrow {
  display: inline-flex; align-items: center; gap: 8px; margin: 0 0 20px;
  font: 600 12.5px var(--mono); color: var(--muted);
  border: 1px solid var(--line); background: var(--surface); padding: 6px 12px; border-radius: 999px;
}
.dot { width: 8px; height: 8px; border-radius: 50%; background: var(--allow); box-shadow: 0 0 0 4px var(--allow-bg); }
h1 { font-size: clamp(34px, 5vw, 56px); line-height: 1.08; letter-spacing: -.025em; margin: 0 0 20px; font-weight: 750; }
h1 em { font-style: normal; color: var(--brand); display: block; }
.lead { font-size: 18px; color: var(--muted); max-width: 56ch; margin: 0 0 28px; }
.lead b { color: var(--ink); }
.cta { display: flex; flex-wrap: wrap; gap: 12px; margin-bottom: 36px; }
.facts { display: flex; flex-wrap: wrap; gap: 28px; margin: 0; padding-top: 24px; border-top: 1px solid var(--line); }
.facts dt { font: 700 24px var(--mono); letter-spacing: -.02em; }
.facts dd { margin: 2px 0 0; font-size: 13.5px; color: var(--muted); max-width: 18ch; line-height: 1.4; }

/* terminal */
.term { background: var(--term-bg); color: var(--term-ink); border-radius: var(--r); box-shadow: var(--shadow); overflow: hidden; border: 1px solid #ffffff14; font-family: var(--mono); font-size: 13px; }
.term-bar { display: flex; align-items: center; gap: 6px; padding: 11px 14px; border-bottom: 1px solid #ffffff12; color: var(--term-dim); font-size: 12px; }
.term-bar i { width: 10px; height: 10px; border-radius: 50%; background: #ffffff22; }
.term-bar span { margin-left: 8px; }
.term-foot { display: flex; justify-content: space-between; gap: 12px; flex-wrap: wrap; padding: 11px 16px; border-top: 1px solid #ffffff12; color: var(--term-dim); font-size: 12px; }
.log { list-style: none; margin: 0; padding: 8px 0; }
.log li { display: grid; grid-template-columns: 92px 1fr; gap: 2px 12px; padding: 10px 16px; opacity: 0; transform: translateY(6px); animation: in .5s forwards; animation-delay: calc(var(--d) * .45s + .3s); }
.log li b { font-weight: 600; color: #fff; }
.log .m { grid-column: 2; color: var(--term-dim); font-size: 12px; }
@keyframes in { to { opacity: 1; transform: none; } }

.tag { display: inline-block; font: 700 11px var(--mono); letter-spacing: .04em; padding: 3px 8px; border-radius: 6px; text-align: center; height: fit-content; }
.tag.allow { color: var(--allow); background: var(--allow-bg); }
.tag.esc { color: var(--esc); background: var(--esc-bg); }
.tag.deny { color: var(--deny); background: var(--deny-bg); }
.term .tag.allow { color: #3ddc97; background: #3ddc9722; }
.term .tag.esc { color: #f3b54a; background: #f3b54a22; }
.term .tag.deny { color: #ff6b6b; background: #ff6b6b22; }

/* sections */
.sec { padding: 96px 0; }
.sec.alt, .band { background: var(--bg-alt); }
.band { padding: 72px 0; border-block: 1px solid var(--line); }
.kicker { font: 650 12.5px var(--mono); text-transform: uppercase; letter-spacing: .09em; color: var(--brand); margin: 0 0 12px; }
h2 { font-size: clamp(26px, 3.4vw, 38px); line-height: 1.15; letter-spacing: -.02em; margin: 0 0 16px; font-weight: 720; max-width: 22em; }
.center h2 { margin-inline: auto; }
h3 { font-size: 19px; line-height: 1.3; margin: 0 0 10px; letter-spacing: -.01em; }
.sub { font-size: 17.5px; color: var(--muted); max-width: 62ch; margin: 0 0 44px; }
.center .sub { margin-inline: auto; margin-bottom: 0; }
.sub b { color: var(--ink); }

.card { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 28px; }
.two { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; }
.three { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; }
.three .card p { color: var(--muted); margin: 0; font-size: 15.5px; }
.tagline { font: 700 13px var(--mono); color: var(--brand); margin: 0 0 8px; letter-spacing: .04em; }
.ticks { list-style: none; margin: 18px 0 0; padding: 0; display: grid; gap: 12px; }
.ticks li { position: relative; padding-left: 26px; color: var(--muted); font-size: 15.5px; }
.ticks li::before { content: ""; position: absolute; left: 0; top: .55em; width: 14px; height: 8px; border-left: 2.5px solid var(--brand); border-bottom: 2.5px solid var(--brand); transform: translateY(-60%) rotate(-45deg); }

/* flow */
.flow { list-style: none; margin: 40px 0; padding: 0; display: grid; grid-template-columns: repeat(4, 1fr); gap: 20px; counter-reset: s; }
.flow li { position: relative; padding-top: 18px; border-top: 2px solid var(--line); }
.flow li:first-child { border-color: var(--brand); }
.flow .n { position: absolute; top: -15px; left: 0; width: 28px; height: 28px; border-radius: 50%; background: var(--brand); color: #fff; font: 700 13px/28px var(--mono); text-align: center; }
.flow li:not(:first-child) .n { background: var(--ink); color: var(--bg); }
.flow p { margin: 0; color: var(--muted); font-size: 15px; }

.diagram { margin: 12px 0 0; background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 20px; }
.diagram svg { width: 100%; height: auto; display: block; }
.diagram figcaption { margin-top: 12px; font-size: 14px; color: var(--muted); text-align: center; }
.diagram .box rect { fill: var(--bg-alt); stroke: var(--line); stroke-width: 1.5; }
.diagram .loc rect { stroke: var(--allow); }
.diagram .gate > rect { fill: color-mix(in srgb, var(--brand) 7%, var(--surface)); stroke: var(--brand); stroke-width: 1.5; stroke-dasharray: 5 4; }
.diagram .chk rect { fill: var(--surface); stroke: var(--line); stroke-width: 1.5; }
.diagram .chk text { fill: var(--ink); font: 600 13px var(--sans); text-anchor: middle; }
.diagram .t1 { fill: var(--ink); font: 700 16px var(--sans); text-anchor: middle; }
.diagram .t2 { fill: var(--muted); font: 12.5px var(--sans); text-anchor: middle; }
.diagram .ln { stroke: var(--muted); stroke-width: 1.8; fill: none; }

/* invariants */
.inv { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; }
.inv article { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 24px; }
.inv b { display: inline-block; font: 700 13px var(--mono); color: var(--brand); background: var(--brand-soft); padding: 3px 9px; border-radius: 6px; margin-bottom: 14px; }
.inv p { margin: 0; color: var(--muted); font-size: 15px; }
.inv .rule { background: var(--ink); border-color: var(--ink); }
.inv .rule h3 { color: var(--bg); }
.inv .rule p { color: color-mix(in srgb, var(--bg) 70%, transparent); }
.inv .rule b { background: color-mix(in srgb, var(--bg) 14%, transparent); color: var(--bg); }

/* ladder */
.ladder { list-style: none; margin: 0; padding: 0; display: grid; grid-template-columns: repeat(5, 1fr); gap: 14px; align-items: end; }
.ladder li { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 18px; min-height: calc(120px + var(--h) * 28px); display: flex; flex-direction: column; border-top: 4px solid color-mix(in srgb, var(--brand) calc(var(--h) * 18% + 10%), var(--line)); }
.ladder b { font: 700 22px var(--mono); }
.ladder h3 { font-size: 15px; margin: 4px 0 8px; color: var(--muted); font-weight: 600; }
.ladder p { margin: 0; font-size: 14px; color: var(--muted); }
.ladder .m4 { border-style: dashed; border-top-style: solid; border-top-color: var(--deny); }
.envelope { margin-top: 28px; display: flex; flex-wrap: wrap; gap: 8px 16px; align-items: baseline; padding: 18px 22px; border: 1px dashed var(--line); border-radius: var(--r); }
.envelope p { margin: 0; color: var(--muted); }
.envelope code { background: var(--surface); border: 1px solid var(--line); padding: 4px 10px; color: var(--ink); }

/* local */
.local { margin-top: 28px; display: grid; grid-template-columns: 1.1fr .9fr; gap: 32px; align-items: center; padding: 32px; border: 1px solid var(--line); border-radius: var(--r); background: var(--surface); }
.local-copy p { color: var(--muted); margin: 0 0 14px; font-size: 15.5px; }
.local-copy h3 { font-size: 22px; }
.local-copy .kicker { margin-bottom: 8px; }
.rule-chip code { display: inline-block; background: var(--brand-soft); color: var(--ink); padding: 8px 12px; border-radius: 8px; word-break: break-word; }
.term.small pre { margin: 0; padding: 16px 18px; overflow-x: auto; line-height: 1.65; }
.term.small code { background: none; padding: 0; color: var(--term-ink); font-size: 12.5px; }
.term .c { color: var(--term-dim); }

/* table */
.tbl { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); overflow: hidden; }
.tr { display: grid; grid-template-columns: 1fr 1.1fr; gap: 16px; padding: 14px 22px; border-top: 1px solid var(--line); align-items: center; font-size: 15.5px; }
.tr.th { border-top: 0; background: var(--bg-alt); font: 650 12.5px var(--mono); text-transform: uppercase; letter-spacing: .06em; color: var(--muted); }
.tr .tag { margin-right: 6px; }
.kill { margin-top: 28px; display: grid; grid-template-columns: 1.2fr .8fr; gap: 32px; }
.kill > div { background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 28px; }
.kill p { color: var(--muted); margin: 0; font-size: 15.5px; }
.three-q ol { margin: 0 0 14px; padding-left: 20px; display: grid; gap: 10px; font-size: 15.5px; }
.three-q .note { font-size: 14px; }

/* roadmap */
.road { list-style: none; margin: 0; padding: 0; display: grid; grid-template-columns: repeat(auto-fit, minmax(210px, 1fr)); gap: 16px; }
.road li { position: relative; background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 20px; display: flex; flex-direction: column; gap: 4px; }
.road b { font: 700 13px var(--mono); color: var(--muted); }
.road h3 { margin: 0 0 4px; font-size: 17px; }
.road p { margin: 0 0 14px; color: var(--muted); font-size: 14.5px; flex: 1; }
.road .st { font: 650 12px var(--mono); color: var(--muted); }
.road .done { border-color: color-mix(in srgb, var(--allow) 45%, var(--line)); }
.road .done .st { color: var(--allow); }
.road .done .st::before { content: "✓ "; }
.road .now { border-color: var(--brand); box-shadow: 0 0 0 3px color-mix(in srgb, var(--brand) 18%, transparent); }
.road .now .st { color: var(--brand); }
.fine { margin: 28px 0 0; font-size: 14px; color: var(--muted); max-width: 80ch; }


/* about */
.about { display: grid; grid-template-columns: 1.15fr .85fr; gap: 56px; align-items: start; }
.about-copy p:not(.kicker) { color: var(--muted); font-size: 17px; max-width: 58ch; margin: 0 0 16px; }
.about-facts { margin-top: 28px; }
.about-pts { list-style: none; margin: 0; padding: 0; display: grid; gap: 14px; }
.about-pts li { background: var(--surface); border: 1px solid var(--line); border-left: 3px solid var(--brand); border-radius: var(--r); padding: 20px 22px; }
.about-pts h3 { font-size: 17px; margin-bottom: 6px; }
.about-pts p { margin: 0; color: var(--muted); font-size: 15px; }

/* CTA + form */
.cta-sec { background: radial-gradient(700px 300px at 50% 0, color-mix(in srgb, var(--brand) 14%, transparent), transparent 70%), var(--bg-alt); border-top: 1px solid var(--line); text-align: center; }
.cta-sec h2 { margin-inline: auto; }
.cta-sec .sub { margin-inline: auto; margin-bottom: 32px; }
.form { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; text-align: left; background: var(--surface); border: 1px solid var(--line); border-radius: var(--r); padding: 26px; box-shadow: var(--shadow); }
.form label { display: grid; gap: 6px; font-size: 14px; font-weight: 600; }
.form .full, .form .btn, .form .status { grid-column: 1 / -1; }
.form input, .form textarea { width: 100%; font: 16px var(--sans); color: var(--ink); background: var(--bg); border: 1px solid var(--line); border-radius: 9px; padding: 11px 12px; }
.form input:focus, .form textarea:focus { outline: 2px solid var(--brand); outline-offset: 0; border-color: transparent; }
.form .hp { position: absolute; left: -9999px; width: 1px; height: 1px; opacity: 0; }
.status { margin: 0; min-height: 1.5em; font-size: 14.5px; }
.status.ok { color: var(--allow); }
.status.err { color: var(--deny); }

.foot { border-top: 1px solid var(--line); padding: 28px 0; font-size: 14px; color: var(--muted); }
.foot-in { display: flex; flex-wrap: wrap; align-items: center; gap: 12px 20px; }
.foot .brand { font-size: 15px; color: var(--ink); }

/* responsive */
@media (max-width: 960px) {
  .hero-grid, .local, .kill, .about { grid-template-columns: 1fr; gap: 32px; }
  .two, .three, .inv { grid-template-columns: 1fr 1fr; }
  .flow { grid-template-columns: 1fr 1fr; row-gap: 32px; }
  .ladder { grid-template-columns: 1fr; }
  .ladder li { min-height: 0; }
  .links { display: none; }
}
@media (max-width: 640px) {
  .sec { padding: 64px 0; }
  .hero { padding: 48px 0 56px; }
  .two, .three, .inv, .flow, .form { grid-template-columns: 1fr; }
  .tr { grid-template-columns: 1fr; gap: 6px; }
  .tr.th span:last-child { display: none; }
  .btn-sm { display: none; }
  .local { padding: 20px; }
  .log li { grid-template-columns: 1fr; }
  .log .m { grid-column: 1; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .log li { animation: none; opacity: 1; transform: none; }
  .btn { transition: none; }
}