/* ===================== 1. Reset & Tokens ===================== */
*, *::before, *::after { box-sizing: border-box; }
body, h1, h2, h3, h4, p, ul, ol, figure, blockquote, address { margin: 0; }
ul, ol { padding: 0; list-style: none; }
img, svg { display: block; max-width: 100%; height: auto; }
button, input, select, textarea { font: inherit; color: inherit; }
a { color: inherit; }
table { border-collapse: collapse; }

:root {
  --pitch-900: #0B1F1A;
  --pitch-800: #10281F;
  --pitch-700: #16352A;
  --ink-950: #070C0A;
  --line-600: #23483C;
  --cyan-400: #35F2D0;
  --amber-500: #FFB03A;
  --mist-100: #E8F1EE;
  --mist-400: #A8BDB6;
  --mist-600: #6E8781;
  --glass-white: rgba(255, 255, 255, 0.08);

  --rail-w: 104px;
  --gap-module: 96px;
  --gap-section: 64px;
  --gap-block: 32px;
  --radius-l: 18px;
  --radius-m: 14px;

  --font-body: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Source Han Sans SC", "Noto Sans CJK SC", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --font-display: "Helvetica Neue", Helvetica, Arial, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --font-mono: ui-monospace, "SF Mono", SFMono-Regular, Menlo, Consolas, "Liberation Mono", "Courier New", monospace;
}

/* ===================== 2. Base ===================== */
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }

body {
  min-height: 100vh;
  padding-left: var(--rail-w);
  background-color: var(--pitch-900);
  background-image:
    radial-gradient(900px 520px at 84% -8%, rgba(53, 242, 208, 0.07), transparent 70%),
    radial-gradient(760px 460px at 3% 104%, rgba(255, 176, 58, 0.045), transparent 72%);
  background-repeat: no-repeat;
  background-attachment: fixed;
  color: var(--mist-400);
  font-family: var(--font-body);
  font-size: 17px;
  font-weight: 400;
  line-height: 1.75;
}

:focus-visible { outline: 2px solid var(--cyan-400); outline-offset: 3px; border-radius: 4px; }

#main-content { display: block; }

/* ===================== 3. Type ===================== */
.bt-display {
  margin: 0;
  font-family: var(--font-display);
  font-size: clamp(44px, 7.5vw, 128px);
  font-weight: 800;
  font-stretch: 87.5%;
  line-height: 0.98;
  letter-spacing: -0.02em;
  color: var(--mist-100);
}
.bt-h2 {
  margin: 0;
  font-family: var(--font-display);
  font-size: clamp(27px, 3.6vw, 46px);
  font-weight: 800;
  font-stretch: 90%;
  line-height: 1.08;
  letter-spacing: -0.02em;
  color: var(--mist-100);
}
.bt-h3 {
  margin: 0;
  font-size: clamp(18px, 1.7vw, 22px);
  font-weight: 700;
  line-height: 1.4;
  letter-spacing: 0.01em;
  color: var(--mist-100);
}
.bt-lead { max-width: 62ch; font-size: clamp(16px, 1.5vw, 19px); line-height: 1.72; color: var(--mist-400); }
.bt-eyebrow {
  display: inline-flex; align-items: center; gap: 10px;
  font-family: var(--font-mono);
  font-size: 12px; letter-spacing: 0.22em; text-transform: uppercase;
  color: var(--cyan-400);
}
.bt-eyebrow::before { content: ""; display: block; width: 22px; height: 1px; background: currentColor; }
.bt-mono { font-family: var(--font-mono); font-variant-numeric: tabular-nums; letter-spacing: 0.02em; }
.bt-anno { writing-mode: vertical-rl; font-size: 12px; letter-spacing: 0.18em; color: var(--mist-600); }

/* ===================== 4. Layout ===================== */
.bt-wrap { width: 100%; max-width: 1240px; margin-inline: auto; padding-inline: clamp(20px, 4vw, 56px); }
.bt-section { padding-block: clamp(48px, 7vw, var(--gap-module)); }
.bt-section--tight { padding-block: clamp(30px, 4vw, var(--gap-section)); }
.bt-rule { height: 1px; border: 0; margin: 0; background: var(--line-600); }
.bt-grid { display: grid; gap: var(--gap-block); }
@media (min-width: 820px) {
  .bt-grid--2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .bt-grid--3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
}

/* ===================== 5. Controls ===================== */
.bt-btn {
  display: inline-flex; align-items: center; gap: 10px;
  padding: 13px 22px;
  border: 1px solid var(--line-600); border-radius: 999px;
  background: transparent; color: var(--mist-100);
  font-size: 14.5px; font-weight: 700; letter-spacing: 0.02em;
  text-decoration: none; cursor: pointer;
  transition: background-color 160ms ease, color 160ms ease, border-color 160ms ease;
}
.bt-btn:hover, .bt-btn:focus-visible { border-color: var(--cyan-400); color: var(--cyan-400); }
.bt-btn--solid { background: var(--cyan-400); border-color: var(--cyan-400); color: var(--pitch-900); }
.bt-btn--solid:hover, .bt-btn--solid:focus-visible { background: var(--mist-100); border-color: var(--mist-100); color: var(--pitch-900); }
.bt-btn--amber { border-color: rgba(255, 176, 58, 0.55); color: var(--amber-500); }
.bt-btn--amber:hover, .bt-btn--amber:focus-visible { background: var(--amber-500); border-color: var(--amber-500); color: var(--pitch-900); }

.bt-copy {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 6px 13px;
  border: 1px solid var(--line-600); border-radius: 999px;
  background: transparent; color: var(--mist-400);
  font-family: var(--font-mono); font-size: 12.5px; letter-spacing: 0.03em;
  cursor: pointer;
  transition: color 160ms ease, border-color 160ms ease, background-color 160ms ease;
}
.bt-copy::after { content: "复制"; font-family: var(--font-body); font-size: 12px; opacity: 0.8; }
.bt-copy:hover { color: var(--cyan-400); border-color: var(--cyan-400); }
.bt-copy[data-copied] { background: var(--cyan-400); border-color: var(--cyan-400); color: var(--pitch-900); }
.bt-copy[data-copied]::after { content: "已复制"; }

.bt-filter { display: flex; flex-wrap: wrap; gap: 8px; }
.bt-filter__btn {
  padding: 8px 16px;
  border: 1px solid var(--line-600); border-radius: 999px;
  background: transparent; color: var(--mist-400);
  font-size: 13.5px; font-weight: 500; letter-spacing: 0.02em;
  cursor: pointer;
  transition: background-color 160ms ease, color 160ms ease, border-color 160ms ease;
}
.bt-filter__btn:hover { color: var(--mist-100); border-color: var(--cyan-400); }
.bt-filter__btn[aria-pressed="true"] { background: var(--cyan-400); border-color: var(--cyan-400); color: var(--pitch-900); font-weight: 700; }

/* ===================== 6. Content components ===================== */
.bt-card {
  padding: clamp(20px, 2.4vw, 28px);
  border: 1px solid var(--line-600); border-radius: var(--radius-l);
  background: var(--pitch-800);
  transition: border-color 160ms ease, background-color 160ms ease;
}
.bt-card:hover { border-color: rgba(53, 242, 208, 0.55); }

.bt-panel {
  padding: clamp(20px, 2.4vw, 30px);
  border: 1px solid var(--line-600); border-radius: var(--radius-m);
  background: var(--pitch-700);
}
.bt-panel__head {
  display: flex; align-items: baseline; justify-content: space-between; gap: 16px;
  padding-bottom: 16px; margin-bottom: 18px;
  border-bottom: 1px solid var(--line-600);
}

.bt-timeband {
  position: relative;
  padding: 30px 0;
  border-top: 1px solid var(--line-600);
  border-bottom: 1px solid var(--line-600);
  background: var(--pitch-800);
  overflow: hidden;
}
.bt-timeband__track { position: relative; height: 2px; margin: 0 clamp(20px, 4vw, 56px); background: var(--line-600); }
.bt-timeband__node {
  position: absolute; top: 50%; width: 9px; height: 9px; border-radius: 50%;
  transform: translate(-50%, -50%);
  background: var(--pitch-800); border: 2px solid var(--cyan-400);
  transition: box-shadow 160ms ease, background-color 160ms ease;
}
.bt-timeband__node:hover { background: var(--cyan-400); box-shadow: 0 0 0 6px rgba(53, 242, 208, 0.15); }
.bt-timeband__node[data-key] { border-color: var(--amber-500); }
.bt-timeband__node[data-key]:hover { background: var(--amber-500); box-shadow: 0 0 0 6px rgba(255, 176, 58, 0.16); }
.bt-timeband__label {
  position: absolute; top: 26px; transform: translateX(-50%);
  font-family: var(--font-mono); font-size: 12px; letter-spacing: 0.06em; color: var(--mist-600);
  white-space: nowrap;
}

.bt-table__wrap { width: 100%; overflow-x: auto; }
.bt-table { width: 100%; min-width: 520px; font-size: 14.5px; }
.bt-table th {
  padding: 12px 14px; text-align: left;
  border-bottom: 1px solid var(--line-600);
  font-size: 12px; font-weight: 700; letter-spacing: 0.14em; color: var(--mist-600);
  white-space: nowrap;
}
.bt-table td { padding: 14px; vertical-align: top; border-bottom: 1px solid rgba(35, 72, 60, 0.6); color: var(--mist-400); }
.bt-table tbody tr { transition: background-color 160ms ease; }
.bt-table tbody tr:hover td { background: rgba(53, 242, 208, 0.04); color: var(--mist-100); }
.bt-num { font-family: var(--font-mono); font-variant-numeric: tabular-nums; letter-spacing: 0.02em; color: var(--mist-100); }

.bt-media {
  position: relative; display: block; overflow: hidden;
  aspect-ratio: 16 / 10;
  border: 1px solid var(--line-600); border-radius: var(--radius-m);
  background: linear-gradient(140deg, var(--pitch-700) 0%, var(--pitch-900) 100%);
}
.bt-media--wide { aspect-ratio: 21 / 9; }
.bt-media--tall { aspect-ratio: 4 / 5; }
.bt-media--square { aspect-ratio: 1 / 1; }
.bt-media img { width: 100%; height: 100%; object-fit: cover; filter: saturate(0.85) contrast(1.05); }
.bt-media__tag {
  position: absolute; left: 14px; bottom: 14px;
  padding: 5px 12px; border: 1px solid var(--line-600); border-radius: 999px;
  background: rgba(7, 12, 10, 0.72);
  font-family: var(--font-mono); font-size: 12px; letter-spacing: 0.08em; color: var(--cyan-400);
}

.bt-note { padding: 4px 0 4px 18px; border-left: 2px solid var(--cyan-400); font-size: 15px; color: var(--mist-400); }
.bt-note--amber { border-left-color: var(--amber-500); }

.bt-tag {
  display: inline-flex; align-items: center; gap: 6px;
  padding: 4px 10px; border: 1px solid var(--line-600); border-radius: 999px;
  font-family: var(--font-mono); font-size: 12px; letter-spacing: 0.08em; color: var(--mist-400);
}
.bt-tag--cyan { border-color: rgba(53, 242, 208, 0.4); color: var(--cyan-400); }
.bt-tag--amber { border-color: rgba(255, 176, 58, 0.45); color: var(--amber-500); }

.bt-crumb {
  display: flex; flex-wrap: wrap; align-items: center; gap: 8px;
  margin-bottom: 24px;
  font-family: var(--font-mono); font-size: 13px; letter-spacing: 0.04em; color: var(--mist-600);
}
.bt-crumb li { display: inline-flex; align-items: center; }
.bt-crumb li::after { content: "/"; margin-left: 8px; color: var(--line-600); }
.bt-crumb li:last-child::after { content: ""; margin: 0; }
.bt-crumb a { color: var(--mist-400); text-decoration: none; border-bottom: 1px solid transparent; transition: color 160ms ease, border-color 160ms ease; }
.bt-crumb a:hover { color: var(--cyan-400); border-bottom-color: var(--cyan-400); }

.bt-anchorlist {
  display: grid; gap: 4px;
  padding: 18px 20px;
  border: 1px solid var(--line-600); border-radius: var(--radius-m);
  background: var(--pitch-800);
}
.bt-anchorlist a {
  display: flex; align-items: baseline; gap: 10px;
  padding: 6px 0;
  border-bottom: 1px dashed transparent;
  color: var(--mist-400); font-size: 14.5px; text-decoration: none;
  transition: color 160ms ease, border-color 160ms ease;
}
.bt-anchorlist a:hover { color: var(--cyan-400); border-bottom-color: rgba(53, 242, 208, 0.4); }

/* ===================== 7. Header ===================== */
.bt-skip {
  position: fixed; top: 8px; left: calc(var(--rail-w) + 8px); z-index: 200;
  padding: 10px 18px;
  border-radius: 999px;
  background: var(--cyan-400); color: var(--pitch-900);
  font-size: 14px; font-weight: 700; text-decoration: none;
  transform: translateY(-180%);
  transition: transform 180ms ease;
}
.bt-skip:focus { transform: none; }

.bt-header {
  position: sticky; top: 0; z-index: 80;
  padding: 16px 28px 0;
}
.bt-header::before {
  content: ""; position: absolute; inset: 0; z-index: -1;
  background: linear-gradient(180deg, rgba(7, 12, 10, 0.94) 0%, rgba(7, 12, 10, 0) 100%);
  opacity: 0; pointer-events: none;
  transition: opacity 200ms ease;
}
.bt-header[data-scrolled]::before { opacity: 1; }

.bt-rail {
  position: fixed; top: 0; left: 0; bottom: 0; width: var(--rail-w); z-index: 90;
  display: flex; flex-direction: column; align-items: center; justify-content: space-between;
  padding: 30px 0 26px;
  background: linear-gradient(180deg, var(--pitch-900) 0%, var(--ink-950) 100%);
  border-right: 1px solid var(--line-600);
}
.bt-rail__brand { display: flex; flex-direction: column; align-items: center; gap: 12px; text-decoration: none; }
.bt-rail__mark {
  width: 8px; height: 8px; border-radius: 2px;
  background: var(--cyan-400);
  box-shadow: 0 0 14px rgba(53, 242, 208, 0.6);
}
.bt-rail__name {
  writing-mode: vertical-rl;
  font-family: var(--font-display);
  font-size: 18px; font-weight: 800; letter-spacing: 0.24em;
  color: var(--mist-100);
}
.bt-rail__brand:hover .bt-rail__name { color: var(--cyan-400); }
.bt-rail__tag {
  writing-mode: vertical-rl;
  font-size: 12px; letter-spacing: 0.18em; color: var(--mist-600);
}
.bt-rail__foot { display: flex; flex-direction: column; align-items: center; gap: 10px; }
.bt-rail__tick { width: 1px; height: 42px; background: linear-gradient(180deg, transparent, var(--cyan-400)); }
.bt-rail__year { font-family: var(--font-mono); font-size: 11px; letter-spacing: 0.1em; color: var(--mist-600); }

.bt-navbar {
  position: relative;
  display: flex; align-items: center; gap: 12px;
  max-width: 1360px;
}

.bt-nav {
  flex: 0 0 auto;
  padding: 6px;
  border: 1px solid var(--line-600); border-radius: 999px;
  background: var(--glass-white);
  -webkit-backdrop-filter: blur(14px) saturate(140%);
  backdrop-filter: blur(14px) saturate(140%);
  box-shadow: 0 12px 34px rgba(0, 0, 0, 0.38);
}
.bt-nav__list { display: flex; gap: 2px; }
.bt-nav__item { list-style: none; }
.bt-nav__link {
  display: block;
  padding: 9px 15px;
  border: 1px solid transparent; border-radius: 999px;
  color: var(--mist-400); font-size: 14px; font-weight: 500; letter-spacing: 0.02em;
  text-decoration: none; white-space: nowrap;
  transition: color 160ms ease, background-color 160ms ease, border-color 160ms ease;
}
.bt-nav__link:hover { color: var(--mist-100); background: rgba(53, 242, 208, 0.09); }
.bt-nav__link[aria-current="page"] { background: var(--cyan-400); color: var(--pitch-900); font-weight: 700; }
.bt-nav__cta { display: none; }

.bt-dateline {
  flex: 1 1 auto; min-width: 0; max-width: 560px;
  display: flex; align-items: center; gap: 6px;
  padding: 5px 6px 5px 12px;
  border: 1px solid var(--line-600); border-radius: 999px;
  background: rgba(11, 31, 26, 0.62);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
}
.bt-dateline__track {
  flex: 1 1 auto; min-width: 0;
  display: flex;
  overflow-x: auto;
  scroll-behavior: smooth;
  scrollbar-width: none;
  -ms-overflow-style: none;
}
.bt-dateline__track::-webkit-scrollbar { display: none; }
.bt-dateline__item {
  display: flex; flex-direction: column; gap: 1px;
  padding: 2px 14px;
  border-left: 1px solid var(--line-600);
  white-space: nowrap;
}
.bt-dateline__item:first-child { border-left: 0; }
.bt-dateline__date {
  font-family: var(--font-mono); font-variant-numeric: tabular-nums;
  font-size: 13px; letter-spacing: 0.04em; color: var(--cyan-400);
}
.bt-dateline__meta { font-size: 11px; letter-spacing: 0.08em; color: var(--mist-600); }
.bt-dateline__step {
  flex: 0 0 auto;
  display: grid; place-items: center;
  width: 26px; height: 26px;
  border: 1px solid var(--line-600); border-radius: 50%;
  background: transparent; color: var(--mist-400);
  font-size: 14px; line-height: 1; cursor: pointer;
  transition: color 160ms ease, border-color 160ms ease, background-color 160ms ease;
}
.bt-dateline__step:hover { color: var(--cyan-400); border-color: var(--cyan-400); background: rgba(53, 242, 208, 0.08); }

.bt-cta {
  flex: 0 0 auto;
  display: inline-flex; align-items: center; gap: 9px;
  padding: 12px 20px;
  border: 1px solid var(--line-600); border-radius: 999px;
  background: var(--pitch-700);
  color: var(--mist-100);
  font-size: 14px; font-weight: 700; letter-spacing: 0.02em; text-decoration: none;
  transition: background-color 160ms ease, color 160ms ease, border-color 160ms ease;
}
.bt-cta::after { content: ""; width: 6px; height: 6px; border-radius: 50%; background: var(--amber-500); transition: background-color 160ms ease; }
.bt-cta:hover { background: var(--cyan-400); border-color: var(--cyan-400); color: var(--pitch-900); }
.bt-cta:hover::after { background: var(--pitch-900); }

.bt-nav-toggle {
  display: none; align-items: center; gap: 9px;
  padding: 10px 16px;
  border: 1px solid var(--line-600); border-radius: 999px;
  background: var(--glass-white);
  color: var(--mist-100);
  font-size: 14px; font-weight: 700; letter-spacing: 0.04em; cursor: pointer;
  transition: border-color 160ms ease, color 160ms ease;
}
.bt-nav-toggle:hover { border-color: var(--cyan-400); color: var(--cyan-400); }
.bt-nav-toggle__bars { display: flex; flex-direction: column; gap: 3px; width: 16px; }
.bt-nav-toggle__bars span { display: block; height: 1.5px; border-radius: 2px; background: currentColor; transition: transform 200ms ease, opacity 200ms ease; }
.bt-header[data-open] .bt-nav-toggle__bars span:nth-child(1) { transform: translateY(4.5px) rotate(45deg); }
.bt-header[data-open] .bt-nav-toggle__bars span:nth-child(2) { opacity: 0; }
.bt-header[data-open] .bt-nav-toggle__bars span:nth-child(3) { transform: translateY(-4.5px) rotate(-45deg); }

/* ===================== 8. Footer ===================== */
.bt-footer {
  margin-top: var(--gap-module);
  border-top: 1px solid var(--line-600);
  background-color: var(--ink-950);
  background-image: repeating-linear-gradient(90deg, rgba(35, 72, 60, 0.22) 0 1px, transparent 1px 140px);
  color: var(--mist-400);
}
.bt-footer__inner {
  display: grid; gap: clamp(32px, 5vw, 64px);
  max-width: 1240px; margin-inline: auto;
  padding: clamp(48px, 6vw, 88px) clamp(20px, 4vw, 56px) 44px;
}
.bt-footer__logo {
  display: block;
  font-family: var(--font-display);
  font-size: clamp(28px, 3.4vw, 44px); font-weight: 800; letter-spacing: -0.01em; line-height: 1;
  color: var(--mist-100);
}
.bt-footer__logo::after { content: "."; color: var(--cyan-400); }
.bt-footer__lede { max-width: 34ch; margin: 14px 0 22px; font-size: 15px; line-height: 1.75; color: var(--mist-400); }
.bt-footer__cta {
  display: inline-flex; align-items: center; gap: 9px;
  padding: 11px 20px;
  border: 1px solid var(--line-600); border-radius: 999px;
  color: var(--mist-100); font-size: 14px; font-weight: 700; letter-spacing: 0.02em; text-decoration: none;
  transition: color 160ms ease, border-color 160ms ease, background-color 160ms ease;
}
.bt-footer__cta:hover { color: var(--pitch-900); background: var(--cyan-400); border-color: var(--cyan-400); }
.bt-footer__contact { display: grid; gap: 6px; margin-top: 24px; font-style: normal; }
.bt-footer__meta { font-family: var(--font-mono); font-size: 12.5px; letter-spacing: 0.02em; color: var(--mist-600); }
.bt-footer__meta--icp { color: var(--mist-400); }
.bt-footer__cols { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 28px; }
.bt-footer__title { margin-bottom: 14px; font-size: 12px; font-weight: 700; letter-spacing: 0.18em; color: var(--mist-600); }
.bt-footer__list { display: grid; gap: 10px; }
.bt-footer__link {
  display: inline-block;
  color: var(--mist-400); font-size: 15px; text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: color 160ms ease, border-color 160ms ease;
}
.bt-footer__link:hover { color: var(--cyan-400); border-bottom-color: var(--cyan-400); }
.bt-footer__bottom {
  display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 12px 28px;
  max-width: 1240px; margin-inline: auto;
  padding: 20px clamp(20px, 4vw, 56px) 34px;
  border-top: 1px solid var(--line-600);
}
.bt-footer__guide {
  color: var(--cyan-400); font-size: 14px; font-weight: 700; letter-spacing: 0.04em; text-decoration: none;
  border-bottom: 1px dashed rgba(53, 242, 208, 0.5);
  transition: color 160ms ease, border-color 160ms ease;
}
.bt-footer__guide:hover { color: var(--mist-100); border-bottom-color: var(--mist-100); }
.bt-footer__legal { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 20px; }

/* ===================== 9. JS-driven ===================== */
.bt-progress {
  position: fixed; top: 0; left: var(--rail-w); right: 0; z-index: 120;
  height: 2px; background: transparent; pointer-events: none;
}
.bt-progress__fill { display: block; width: 0; height: 100%; background: linear-gradient(90deg, var(--cyan-400) 0%, var(--amber-500) 100%); transition: width 120ms linear; }

html.bt-js [data-reveal] {
  opacity: 0; transform: translateY(16px);
  transition: opacity 500ms ease, transform 500ms ease;
}
html.bt-js [data-reveal].is-visible { opacity: 1; transform: none; }
[data-filter-item][hidden] { display: none; }

/* ===================== 10. Responsive ===================== */
@media (min-width: 960px) {
  .bt-footer__inner { grid-template-columns: minmax(260px, 1.15fr) 2fr; }
}

@media (max-width: 1180px) {
  .bt-dateline { display: none; }
  .bt-navbar { max-width: none; }
}

@media (max-width: 1080px) {
  :root { --rail-w: 0px; }
  body { padding-left: 0; }
  .bt-progress { left: 0; }
  .bt-skip { left: 8px; }
  .bt-header { display: flex; flex-wrap: wrap; align-items: center; gap: 12px; padding: 12px 16px 0; }
  .bt-rail {
    position: static; width: auto; height: auto; flex-direction: row; align-items: center; gap: 10px;
    padding: 9px 16px;
    border: 1px solid var(--line-600); border-radius: 999px;
    background: var(--glass-white);
    -webkit-backdrop-filter: blur(12px);
    backdrop-filter: blur(12px);
  }
  .bt-rail__brand { flex-direction: row; align-items: center; gap: 8px; }
  .bt-rail__name { writing-mode: horizontal-tb; font-size: 15px; font-weight: 800; letter-spacing: 0.1em; }
  .bt-rail__tag, .bt-rail__foot { display: none; }
  .bt-navbar { flex: 1 1 auto; }
}

@media (max-width: 900px) {
  .bt-nav-toggle { display: inline-flex; margin-left: auto; }
  .bt-cta { display: none; }
  .bt-nav {
    position: absolute; top: calc(100% + 12px); left: 16px; right: 16px;
    display: none;
    padding: 12px;
    border-radius: 20px;
    background: rgba(11, 31, 26, 0.97);
    box-shadow: 0 26px 54px rgba(0, 0, 0, 0.55);
  }
  .bt-header[data-open] .bt-nav { display: block; }
  .bt-nav__list { flex-direction: column; gap: 4px; }
  .bt-nav__link { padding: 13px 16px; border-radius: 12px; font-size: 15px; }
  .bt-nav__cta {
    display: flex; align-items: center; justify-content: center;
    margin-top: 10px; padding: 13px 16px;
    border-radius: 12px;
    background: var(--cyan-400); color: var(--pitch-900);
    font-size: 15px; font-weight: 700; text-decoration: none;
    transition: background-color 160ms ease, color 160ms ease;
  }
  .bt-nav__cta:hover { background: var(--mist-100); }
  .bt-footer__cols { grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 32px 24px; }
}

@media (max-width: 640px) {
  body { font-size: 16px; }
  .bt-footer__cols { grid-template-columns: minmax(0, 1fr); }
  .bt-footer__bottom { flex-direction: column; align-items: flex-start; }
  .bt-nav-toggle__label { display: none; }
  .bt-table { min-width: 440px; }
}

/* ===================== 11. Motion & a11y ===================== */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }
  html.bt-js [data-reveal] { opacity: 1; transform: none; }
}