/* Global 中文 | EN toggle — homepage header, article site-nav, fallback float */
.bt-lang-toggle {
  --bt-lang-fg: currentColor;
  --bt-lang-bg: #fff;
  display: inline-flex;
  align-items: stretch;
  flex: 0 0 auto;
  border: 1px solid var(--bt-lang-fg);
  background: transparent;
  font-family: ui-monospace, SFMono-Regular, "JetBrains Mono", monospace;
  font-size: 10px;
  font-weight: 500;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  line-height: 1.2;
  user-select: none;
  -webkit-user-select: none;
}
.bt-lang-toggle button {
  appearance: none;
  -webkit-appearance: none;
  margin: 0;
  border: 0;
  background: transparent;
  color: var(--bt-lang-fg);
  padding: 6px 10px;
  cursor: pointer;
  font: inherit;
  letter-spacing: inherit;
  text-transform: inherit;
}
.bt-lang-toggle button + button {
  border-left: 1px solid var(--bt-lang-fg);
}
.bt-lang-toggle button:hover:not([aria-pressed="true"]) {
  background: rgba(127, 127, 127, 0.12);
}
.bt-lang-toggle button[aria-pressed="true"] {
  background: rgba(127, 127, 127, 0.2);
  font-weight: 700;
}
.bt-lang-toggle button:focus-visible {
  outline: 2px solid #13715c;
  outline-offset: 2px;
  z-index: 1;
}

.topbar-end .bt-lang-toggle {
  --bt-lang-fg: #090b0c;
  --bt-lang-bg: #fff;
}
.topbar-end .bt-lang-toggle button[aria-pressed="true"] {
  background: var(--bt-lang-fg);
  color: var(--bt-lang-bg);
  font-weight: 500;
}

.site-nav .bt-lang-toggle {
  --bt-lang-fg: currentColor;
  --bt-lang-bg: var(--bg, var(--paper, #111414));
}

nav.topbar .bt-lang-toggle {
  margin-left: 8px;
}
nav.topbar .bt-lang-toggle button[aria-pressed="true"] {
  background: #f2f3f5;
  color: #050507;
  font-weight: 500;
}

.bt-lang-toggle--float {
  position: fixed;
  top: 12px;
  right: 12px;
  z-index: 9999;
  --bt-lang-fg: #090b0c;
  --bt-lang-bg: #fff;
  background: #fff;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.12);
}

.topbar-end {
  display: flex;
  align-items: center;
  gap: 18px;
  min-width: 0;
  margin-left: auto;
}

@media (max-width: 820px) {
  .topbar-end {
    gap: 12px;
  }
}

@media print {
  .bt-lang-toggle { display: none; }
}