/* =========================================================
   贝投主页 · 共享样式 /assets/site.css
   结构：reset → 变量 → 排版 → 容器 → 通用组件 → 页头 → 页脚 → 响应式
   ========================================================= */

/* ---------- reset ---------- */
*,
*::before,
*::after { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 128px;
}

body {
  margin: 0;
  background-color: #F5F2EA;
  color: #101418;
  font-family: var(--bt-sans);
  font-size: 16px;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

h1, h2, h3, h4, h5, h6, p, ul, ol, figure, blockquote, dl, dd {
  margin: 0;
}

ul, ol {
  padding: 0;
  list-style: none;
}

img, svg, video {
  display: block;
  max-width: 100%;
  height: auto;
}

a { color: inherit; }

button {
  font: inherit;
  color: inherit;
  margin: 0;
}

table { border-collapse: collapse; width: 100%; }

:focus-visible {
  outline: 2px solid #B87333;
  outline-offset: 2px;
}

::selection {
  background-color: #E1C7A3;
  color: #0B1F33;
}

/* ---------- 变量 ---------- */
:root {
  --bt-ink: #0B1F33;
  --bt-night: #14324F;
  --bt-gold: #B87333;
  --bt-gold-deep: #8C5522;
  --bt-gold-soft: #E1C7A3;
  --bt-mist: #6F8F8A;
  --bt-mist-soft: #DCE7E3;
  --bt-silver: #C8CDD2;
  --bt-paper: #F5F2EA;
  --bt-black: #101418;

  --bt-serif: "Noto Serif SC", "Source Han Serif SC", "Songti SC", "STSong", "SimSun", Georgia, serif;
  --bt-sans: "Noto Sans SC", "Source Han Sans SC", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --bt-mono: "JetBrains Mono", "Roboto Mono", ui-monospace, SFMono-Regular, Menlo, Consolas, "Courier New", monospace;

  --bt-ease: cubic-bezier(.22, .75, .28, 1);
  --bt-dur: 180ms;
  --bt-shadow: 0 22px 40px -30px rgba(11, 31, 51, .55);
}

/* ---------- 中文排版基座 ---------- */
.bt-mono {
  font-family: var(--bt-mono);
  font-size: 13px;
  letter-spacing: .04em;
}

.bt-prose {
  max-width: 62ch;
  font-size: 17px;
  line-height: 1.8;
  color: #1c2530;
  word-break: break-word;
}

.bt-prose > * + * { margin-top: 1.05em; }

.bt-prose h2,
.bt-prose h3,
.bt-prose h4 {
  font-family: var(--bt-serif);
  font-weight: 600;
  line-height: 1.28;
  color: var(--bt-ink);
  letter-spacing: -.01em;
}

.bt-prose h2 { font-size: clamp(1.5rem, 2.4vw, 2rem); margin-top: 2.2em; }
.bt-prose h3 { font-size: 1.24rem; margin-top: 1.9em; }
.bt-prose h4 { font-size: 1.06rem; margin-top: 1.6em; }

.bt-prose ul { list-style: none; }
.bt-prose ul li {
  position: relative;
  padding-left: 22px;
}
.bt-prose ul li + li { margin-top: .5em; }
.bt-prose ul li::before {
  content: "";
  position: absolute;
  left: 2px;
  top: .72em;
  width: 8px;
  height: 8px;
  background-color: var(--bt-gold);
  clip-path: polygon(50% 0, 100% 50%, 50% 100%, 0 50%);
}
.bt-prose ol { list-style: decimal; padding-left: 1.4em; }
.bt-prose ol li + li { margin-top: .5em; }

.bt-prose blockquote {
  padding: 16px 22px;
  background-color: var(--bt-gold-soft);
  border-left: 3px solid var(--bt-gold);
  color: var(--bt-ink);
  font-family: var(--bt-serif);
  font-size: 1.02rem;
}

.bt-prose a {
  color: var(--bt-gold-deep);
  text-decoration: underline;
  text-underline-offset: 3px;
}
.bt-prose a:hover { color: var(--bt-ink); }

.bt-prose code {
  font-family: var(--bt-mono);
  font-size: .88em;
  padding: 2px 6px;
  background-color: var(--bt-mist-soft);
  color: var(--bt-ink);
}

/* ---------- 容器 ---------- */
.bt-container {
  width: 100%;
  max-width: 1180px;
  margin-left: auto;
  margin-right: auto;
  padding-left: 20px;
  padding-right: 20px;
}

.bt-slash {
  height: 6px;
  border: 0;
  margin: 0;
  background-image: repeating-linear-gradient(115deg, var(--bt-silver) 0 1px, transparent 1px 9px);
}

/* ---------- 按钮 ---------- */
.bt-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: .5em;
  padding: 13px 22px;
  border: 1px solid transparent;
  background-color: transparent;
  font-size: 15px;
  font-weight: 500;
  line-height: 1.2;
  text-decoration: none;
  cursor: pointer;
  transition: background-color var(--bt-dur) var(--bt-ease),
              color var(--bt-dur) var(--bt-ease),
              border-color var(--bt-dur) var(--bt-ease),
              transform var(--bt-dur) var(--bt-ease);
}

.bt-btn--gold {
  background-color: var(--bt-gold);
  color: #FFFFFF;
  border-color: var(--bt-gold);
}
.bt-btn--gold:hover {
  background-color: var(--bt-gold-deep);
  border-color: var(--bt-gold-deep);
}
.bt-btn--gold:active { transform: translateY(1px); }

.bt-btn--ghost {
  background-color: transparent;
  color: var(--bt-ink);
  border-color: var(--bt-ink);
}
.bt-btn--ghost:hover {
  background-color: var(--bt-ink);
  color: var(--bt-paper);
}

.bt-btn--quiet {
  padding: 6px 0;
  color: var(--bt-gold-deep);
  border: 0;
  border-bottom: 1px solid rgba(184, 115, 51, .5);
}
.bt-btn--quiet:hover {
  color: var(--bt-ink);
  border-bottom-color: var(--bt-ink);
}

/* ---------- 面包屑 ---------- */
.bt-crumbs { padding: 18px 0 0; }

.bt-crumbs__list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  font-family: var(--bt-mono);
  font-size: 12px;
  letter-spacing: .04em;
  color: #5b6672;
}

.bt-crumbs__item a {
  text-decoration: none;
  border-bottom: 1px solid rgba(111, 143, 138, .55);
}
.bt-crumbs__item a:hover {
  color: var(--bt-gold-deep);
  border-bottom-color: var(--bt-gold);
}
.bt-crumbs__item [aria-current="page"] { color: var(--bt-ink); }

.bt-crumbs__sep {
  color: var(--bt-silver);
  user-select: none;
}

/* ---------- 章节骨架 ---------- */
.bt-section {
  padding: 56px 0;
  border-top: 1px solid var(--bt-silver);
}
.bt-section--plain { border-top: 0; }

.bt-section__head {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 8px 18px;
  margin-bottom: 26px;
}

.bt-section__index {
  font-family: var(--bt-mono);
  font-size: 12px;
  letter-spacing: .18em;
  color: var(--bt-gold-deep);
  white-space: nowrap;
}

.bt-section__title {
  font-family: var(--bt-serif);
  font-weight: 600;
  font-size: clamp(1.6rem, 3.2vw, 2.5rem);
  line-height: 1.16;
  letter-spacing: -.015em;
  color: var(--bt-ink);
  margin: 0;
}

.bt-section__lead {
  flex: 1 1 320px;
  max-width: 62ch;
  color: #3a4550;
  font-size: 16px;
}

/* ---------- 网格 ---------- */
.bt-grid {
  display: grid;
  gap: 22px;
  grid-template-columns: 1fr;
}

@media (min-width: 700px) {
  .bt-grid--2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .bt-grid--3 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (min-width: 1040px) {
  .bt-grid--3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
}

/* ---------- 跳转卡 ---------- */
.bt-card {
  position: relative;
  display: flex;
  flex-direction: column;
  gap: 10px;
  padding: 22px 22px 24px;
  background-color: #FFFFFF;
  border: 1px solid var(--bt-silver);
  text-decoration: none;
  color: inherit;
  clip-path: polygon(0 0, calc(100% - 18px) 0, 100% 18px, 100% 100%, 0 100%);
  transition: transform var(--bt-dur) var(--bt-ease),
              box-shadow var(--bt-dur) var(--bt-ease),
              border-color var(--bt-dur) var(--bt-ease);
}

.bt-card:hover {
  transform: translateY(-3px);
  border-color: var(--bt-mist);
  box-shadow: var(--bt-shadow);
}

.bt-card:focus-visible {
  outline: none;
  box-shadow: inset 0 0 0 2px var(--bt-gold);
}

.bt-card__label {
  font-family: var(--bt-mono);
  font-size: 11px;
  letter-spacing: .12em;
  color: var(--bt-mist);
}

.bt-card__title {
  font-family: var(--bt-serif);
  font-weight: 600;
  font-size: 1.2rem;
  line-height: 1.35;
  color: var(--bt-ink);
}

.bt-card__text {
  font-size: 15px;
  line-height: 1.75;
  color: #3a4550;
}

.bt-card__meta {
  font-family: var(--bt-mono);
  font-size: 12px;
  letter-spacing: .04em;
  color: #6b7681;
}

.bt-card__foot {
  margin-top: auto;
  padding-top: 12px;
  border-top: 1px solid var(--bt-silver);
  font-family: var(--bt-mono);
  font-size: 12px;
  letter-spacing: .06em;
  color: var(--bt-gold-deep);
}

/* ---------- 标签 ---------- */
.bt-tag {
  display: inline-block;
  padding: 4px 10px;
  font-family: var(--bt-mono);
  font-size: 11px;
  letter-spacing: .08em;
  line-height: 1.6;
  background-color: var(--bt-mist-soft);
  color: #2F4A47;
  border: 1px solid rgba(111, 143, 138, .38);
}

.bt-tag--gold {
  background-color: var(--bt-gold-soft);
  color: #6B3F16;
  border-color: rgba(184, 115, 51, .42);
}

/* ---------- 提示框 ---------- */
.bt-note {
  padding: 16px 20px;
  background-color: var(--bt-mist-soft);
  border-left: 3px solid var(--bt-mist);
  font-size: 14.5px;
  line-height: 1.8;
  color: #26383A;
}
.bt-note strong { color: var(--bt-ink); }

/* ---------- 时间轴 ---------- */
.bt-axis {
  border-left: 1px solid var(--bt-silver);
}

.bt-axis__item {
  position: relative;
  padding: 0 0 22px 20px;
}
.bt-axis__item:last-child { padding-bottom: 0; }

.bt-axis__item::before {
  content: "";
  position: absolute;
  left: -5px;
  top: 7px;
  width: 9px;
  height: 9px;
  background-color: var(--bt-gold);
  clip-path: polygon(50% 0, 100% 50%, 50% 100%, 0 50%);
}

.bt-axis__label {
  display: block;
  font-family: var(--bt-mono);
  font-size: 11px;
  letter-spacing: .1em;
  color: var(--bt-gold-deep);
}

.bt-axis__text {
  display: block;
  font-size: 14.5px;
  line-height: 1.7;
  color: #3a4550;
}

/* ---------- 图片容器（页面阶段放图） ---------- */
.bt-figure {
  display: block;
  width: 100%;
}

.bt-figure__frame {
  position: relative;
  display: block;
  aspect-ratio: 16 / 10;
  overflow: hidden;
  border: 1px solid var(--bt-silver);
  background-color: var(--bt-mist-soft);
  background-image: repeating-linear-gradient(115deg, rgba(111, 143, 138, .16) 0 1px, transparent 1px 10px);
  clip-path: polygon(0 0, calc(100% - 22px) 0, 100% 22px, 100% 100%, 0 100%);
}

.bt-figure__img {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.bt-figure__caption {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  margin-top: 10px;
  padding-top: 9px;
  border-top: 1px solid var(--bt-silver);
  font-family: var(--bt-mono);
  font-size: 12px;
  letter-spacing: .03em;
  line-height: 1.7;
  color: #5b6672;
}

.bt-figure__caption::before {
  content: "";
  flex: 0 0 14px;
  height: 2px;
  margin-top: .7em;
  background-color: var(--bt-gold);
}

.bt-figure--wide .bt-figure__frame { aspect-ratio: 21 / 9; }
.bt-figure--tall .bt-figure__frame { aspect-ratio: 3 / 4; }

/* =========================================================
   页头
   ========================================================= */
.bt-header {
  position: sticky;
  top: 0;
  z-index: 60;
  background-color: var(--bt-paper);
}

.bt-skip {
  position: absolute;
  left: 16px;
  top: -64px;
  z-index: 90;
  padding: 10px 18px;
  background-color: var(--bt-gold);
  color: #101418;
  font-size: 14px;
  font-weight: 500;
  text-decoration: none;
  transition: top var(--bt-dur) var(--bt-ease);
}
.bt-skip:focus { top: 10px; }

.bt-header__bar {
  background-color: var(--bt-ink);
  color: var(--bt-paper);
}

.bt-header__barInner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  min-height: 58px;
  padding-top: 9px;
  padding-bottom: 9px;
  transition: min-height var(--bt-dur) var(--bt-ease),
              padding var(--bt-dur) var(--bt-ease);
}

.bt-header.is-pinned .bt-header__barInner {
  min-height: 44px;
  padding-top: 4px;
  padding-bottom: 4px;
}

.bt-brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  text-decoration: none;
  color: inherit;
  min-width: 0;
}

.bt-brand__mark {
  position: relative;
  flex: 0 0 24px;
  width: 24px;
  height: 24px;
  border: 1px solid rgba(245, 242, 234, .34);
}

.bt-brand__dot {
  position: absolute;
  inset: 5px;
  background-color: var(--bt-gold);
  clip-path: polygon(50% 0, 100% 50%, 50% 100%, 0 50%);
  transition: transform 220ms var(--bt-ease);
}

.bt-brand:hover .bt-brand__dot,
.bt-brand:focus-visible .bt-brand__dot {
  transform: rotate(45deg) scale(.86);
}

.bt-brand__text {
  display: block;
  min-width: 0;
}

.bt-brand__name {
  display: block;
  font-family: var(--bt-serif);
  font-size: 17px;
  font-weight: 600;
  line-height: 1.2;
  letter-spacing: .02em;
}

.bt-brand__line {
  display: block;
  font-family: var(--bt-mono);
  font-size: 11px;
  line-height: 1.5;
  letter-spacing: .06em;
  color: rgba(245, 242, 234, .62);
}

.bt-header__meta {
  display: flex;
  align-items: center;
  gap: 18px;
  min-width: 0;
}

.bt-version {
  flex: none;
  padding: 4px 10px;
  font-family: var(--bt-mono);
  font-size: 11px;
  letter-spacing: .08em;
  line-height: 1.6;
  color: var(--bt-gold-soft);
  border: 1px solid rgba(184, 115, 51, .62);
  white-space: nowrap;
}

.bt-utility__list {
  display: flex;
  flex-wrap: wrap;
  gap: 18px;
}

.bt-utility__link {
  font-size: 12.5px;
  letter-spacing: .04em;
  color: rgba(245, 242, 234, .72);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: color var(--bt-dur) var(--bt-ease),
              border-color var(--bt-dur) var(--bt-ease);
}
.bt-utility__link:hover {
  color: var(--bt-gold-soft);
  border-bottom-color: var(--bt-gold);
}

.bt-header__navRow {
  position: relative;
  background-color: var(--bt-paper);
  border-bottom: 1px solid var(--bt-silver);
}

.bt-header__navInner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  min-height: 54px;
}

.bt-nav-toggle {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 9px 13px;
  background-color: transparent;
  border: 1px solid var(--bt-silver);
  color: var(--bt-ink);
  font-family: var(--bt-mono);
  font-size: 12px;
  letter-spacing: .12em;
  cursor: pointer;
  transition: border-color var(--bt-dur) var(--bt-ease),
              background-color var(--bt-dur) var(--bt-ease);
}
.bt-nav-toggle:hover { border-color: var(--bt-mist); background-color: rgba(220, 231, 227, .5); }

.bt-nav-toggle__bars {
  position: relative;
  display: block;
  width: 16px;
  height: 2px;
  background-color: var(--bt-ink);
  transition: background-color var(--bt-dur) var(--bt-ease);
}
.bt-nav-toggle__bars::before,
.bt-nav-toggle__bars::after {
  content: "";
  position: absolute;
  left: 0;
  width: 16px;
  height: 2px;
  background-color: var(--bt-ink);
  transition: transform var(--bt-dur) var(--bt-ease);
}
.bt-nav-toggle__bars::before { top: -5px; }
.bt-nav-toggle__bars::after { top: 5px; }

.bt-nav-toggle[aria-expanded="true"] .bt-nav-toggle__bars { background-color: transparent; }
.bt-nav-toggle[aria-expanded="true"] .bt-nav-toggle__bars::before { transform: translateY(5px) rotate(45deg); }
.bt-nav-toggle[aria-expanded="true"] .bt-nav-toggle__bars::after { transform: translateY(-5px) rotate(-45deg); }

.bt-nav-toggle__text { line-height: 1; }

.bt-nav__list {
  display: flex;
  flex-direction: column;
  gap: 0;
}

.bt-nav__item { border-bottom: 1px solid var(--bt-silver); }
.bt-nav__item:last-child { border-bottom: 0; }

.bt-nav__link {
  position: relative;
  display: block;
  padding: 14px 2px;
  font-size: 16px;
  font-weight: 500;
  text-decoration: none;
  color: var(--bt-ink);
  transition: color var(--bt-dur) var(--bt-ease);
}

.bt-nav__link::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: 10px;
  width: 24px;
  height: 2px;
  background-color: var(--bt-gold);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform var(--bt-dur) var(--bt-ease);
}

.bt-nav__link:hover { color: var(--bt-gold-deep); }
.bt-nav__link:hover::after { transform: scaleX(1); }

.bt-nav__link[aria-current="page"] { color: var(--bt-gold-deep); }
.bt-nav__link[aria-current="page"]::after { transform: scaleX(1); }

.bt-nav {
  display: none;
}

.bt-nav[data-open] {
  display: block;
  position: absolute;
  left: 0;
  right: 0;
  top: 100%;
  max-height: calc(100vh - 130px);
  overflow-y: auto;
  padding: 6px 20px 20px;
  background-color: var(--bt-paper);
  border-top: 1px solid var(--bt-silver);
  border-bottom: 1px solid var(--bt-silver);
  box-shadow: 0 22px 34px -26px rgba(11, 31, 51, .55);
}

.bt-header__cta {
  flex: none;
  padding: 10px 16px;
  font-size: 13px;
}

.bt-progress {
  position: absolute;
  left: 0;
  bottom: 0;
  z-index: 5;
  width: 100%;
  height: 2px;
  background-color: var(--bt-gold);
  transform: scaleX(0);
  transform-origin: left center;
  pointer-events: none;
}

.bt-totop {
  position: fixed;
  right: 20px;
  bottom: 20px;
  z-index: 70;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 14px;
  background-color: var(--bt-ink);
  color: var(--bt-paper);
  border: 1px solid rgba(184, 115, 51, .55);
  font-family: var(--bt-mono);
  font-size: 11px;
  letter-spacing: .1em;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(8px);
  transition: opacity var(--bt-dur) var(--bt-ease),
              transform var(--bt-dur) var(--bt-ease),
              visibility var(--bt-dur) var(--bt-ease),
              border-color var(--bt-dur) var(--bt-ease);
}

.bt-totop[data-visible] {
  opacity: 1;
  visibility: visible;
  transform: none;
}

.bt-totop:hover { border-color: var(--bt-gold); }

/* =========================================================
   页脚
   ========================================================= */
.bt-footer {
  margin-top: clamp(48px, 8vw, 96px);
  background-color: var(--bt-night);
  color: var(--bt-paper);
}

.bt-footer__band {
  background-color: var(--bt-ink);
  border-bottom: 1px solid rgba(200, 205, 210, .14);
}

.bt-footer__bandInner { display: block; }

.bt-band__cell {
  display: flex;
  align-items: baseline;
  gap: 12px;
  padding: 14px 0;
  border-bottom: 1px solid rgba(200, 205, 210, .14);
}
.bt-band__cell:last-child { border-bottom: 0; }

.bt-band__key {
  flex: none;
  font-family: var(--bt-mono);
  font-size: 11px;
  letter-spacing: .16em;
  color: var(--bt-gold);
}

.bt-band__val {
  font-size: 13px;
  line-height: 1.7;
  color: rgba(245, 242, 234, .78);
}

.bt-footer__main { padding: 48px 0 40px; }

.bt-footer__grid {
  display: grid;
  gap: 32px;
  grid-template-columns: 1fr;
}

.bt-footer__brandName {
  font-family: var(--bt-serif);
  font-size: 22px;
  font-weight: 600;
  line-height: 1.3;
  letter-spacing: .02em;
  color: var(--bt-paper);
}

.bt-footer__note {
  margin-top: 12px;
  max-width: 34ch;
  font-size: 13px;
  line-height: 1.9;
  color: rgba(245, 242, 234, .6);
}

.bt-footer__title {
  margin-bottom: 14px;
  font-family: var(--bt-mono);
  font-size: 11px;
  letter-spacing: .16em;
  color: var(--bt-gold-soft);
}

.bt-footer__list { display: block; }

.bt-footer__link {
  display: inline-block;
  padding: 5px 0;
  font-size: 14px;
  text-decoration: none;
  color: rgba(245, 242, 234, .78);
  border-bottom: 1px solid transparent;
  transition: color var(--bt-dur) var(--bt-ease),
              border-color var(--bt-dur) var(--bt-ease);
}
.bt-footer__link:hover {
  color: var(--bt-paper);
  border-bottom-color: var(--bt-gold);
}

.bt-contact { display: grid; gap: 10px; }

.bt-contact__row {
  display: grid;
  grid-template-columns: 46px minmax(0, 1fr);
  gap: 10px;
  align-items: start;
}

.bt-contact__key {
  font-family: var(--bt-mono);
  font-size: 11px;
  letter-spacing: .1em;
  line-height: 1.9;
  color: var(--bt-mist);
}

.bt-contact__val {
  font-size: 13.5px;
  line-height: 1.85;
  color: rgba(245, 242, 234, .78);
  word-break: break-word;
}

.bt-footer__legal {
  border-top: 1px solid rgba(200, 205, 210, .14);
  padding: 18px 0 24px;
}

.bt-footer__legalInner {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 8px 24px;
}

.bt-footer__legalText {
  font-family: var(--bt-mono);
  font-size: 12px;
  letter-spacing: .04em;
  line-height: 1.8;
  color: rgba(245, 242, 234, .55);
}

/* =========================================================
   断点：≥600 / ≥768 / ≥900 / ≥1040
   ========================================================= */
@media (max-width: 900px) {
  .bt-totop { right: 14px; bottom: 14px; }
}

@media (max-width: 560px) {
  .bt-brand__line { display: none; }
  .bt-header__meta { gap: 10px; }
  .bt-version { font-size: 10px; padding: 3px 8px; }
}

@media (max-width: 460px) {
  .bt-utility { display: none; }
  .bt-header__cta { padding: 9px 12px; font-size: 12.5px; }
  .bt-crumbs { padding-top: 14px; }
}

@media (min-width: 600px) {
  .bt-container { padding-left: 28px; padding-right: 28px; }
}

@media (min-width: 768px) {
  .bt-container { padding-left: 32px; padding-right: 32px; }

  .bt-footer__bandInner {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }
  .bt-band__cell {
    padding: 18px 24px;
    border-bottom: 0;
    border-left: 1px solid rgba(200, 205, 210, .14);
  }
  .bt-band__cell:first-child {
    padding-left: 0;
    border-left: 0;
  }

  .bt-footer__grid { grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 36px; }

  .bt-section { padding: 68px 0; }
}

@media (min-width: 900px) {
  .bt-nav-toggle { display: none; }

  .bt-header__navInner { min-height: 58px; }

  .bt-nav {
    display: block;
    position: static;
    flex: 1 1 auto;
    max-height: none;
    overflow: visible;
    padding: 0;
    background-color: transparent;
    border: 0;
    box-shadow: none;
  }

  .bt-nav__list {
    flex-direction: row;
    gap: 0 28px;
  }

  .bt-nav__item { border-bottom: 0; }

  .bt-nav__link {
    padding: 18px 0;
    font-size: 15px;
  }

  .bt-nav__link::after {
    left: 0;
    right: 0;
    width: auto;
    bottom: 12px;
  }
}

@media (min-width: 1000px) {
  .bt-footer__grid {
    grid-template-columns: 1.5fr .85fr .85fr .8fr 1.35fr;
    gap: 30px;
  }
}

/* ---------- 动效偏好 ---------- */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }

  *,
  *::before,
  *::after {
    animation-duration: .001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: .001ms !important;
  }

  .bt-card:hover { transform: none; }
  .bt-brand:hover .bt-brand__dot { transform: none; }
}