/* ───── nav.css — 顶部导航 ─────
   固定顶部、默认透明;滚动后(#nav.scrolled,由 nav.js 加)上毛玻璃 + 底部细线。
   DOM:#nav > .nav-inner > (.logo[.logo-dot] + .nav-toggle + .nav-links[a... .theme-toggle]) */

#nav {
  position: fixed;
  inset: 0 0 auto 0;
  z-index: 100;
  background: transparent;
  border-bottom: 1px solid transparent;
  transition: background .4s var(--ease), border-color .4s var(--ease),
    backdrop-filter .4s var(--ease);
}

/* 滚动后:毛玻璃 + 细线 */
#nav.scrolled {
  background: var(--nav-bg);
  -webkit-backdrop-filter: saturate(180%) blur(20px);
  backdrop-filter: saturate(180%) blur(20px);
  border-bottom-color: var(--line);
}

/* nav 横跨整屏,内容居中收窄 */
.nav-inner {
  max-width: var(--page-max);
  margin: 0 auto;
  padding: 14px 22px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

/* logo + 小圆点 */
.logo {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  font-size: 17px;
  font-weight: 680;
  letter-spacing: -.3px;
  color: var(--text);
  text-decoration: none;
  transition: opacity .2s var(--ease);
}
.logo:hover { opacity: .72; }
.logo-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--accent);
  flex: none;
}

/* 桌面横排链接 */
.nav-links {
  display: flex;
  align-items: center;
  gap: 26px;
}
.nav-links a {
  position: relative;
  font-size: 14px;
  color: var(--text-2);
  text-decoration: none;
  padding: 4px 0;
  transition: color .25s var(--ease);
}
/* 下划线动画 */
.nav-links a::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -1px;
  height: 1.5px;
  width: 100%;
  background: var(--accent);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform .3s var(--ease);
}
.nav-links a:hover,
.nav-links a.active { color: var(--accent); }
.nav-links a:hover::after,
.nav-links a.active::after { transform: scaleX(1); }

/* 主题切换:液态玻璃圆形按钮 */
.theme-toggle {
  position: relative;
  overflow: hidden;
  isolation: isolate;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 40px;
  height: 40px;
  border-radius: 50%;
  border: 1px solid var(--glass-edge);
  background: var(--glass-bg);
  -webkit-backdrop-filter: blur(var(--glass-blur)) saturate(180%);
  backdrop-filter: blur(var(--glass-blur)) saturate(180%);
  box-shadow: inset 0 1px 0 var(--glass-sheen);
  color: var(--text-2);
  font-size: 16px;
  line-height: 1;
  cursor: pointer;
  transition: color .25s var(--ease), border-color .25s var(--ease),
    background .25s var(--ease), transform .25s var(--ease);
}
.theme-toggle::before {
  content: ""; position: absolute; inset: 0; z-index: -1;
  background: radial-gradient(40px circle at var(--gx, 50%) var(--gy, 50%), var(--glass-sheen), transparent 60%);
  opacity: 0; transition: opacity .35s var(--ease); pointer-events: none;
}
.theme-toggle:hover::before { opacity: 1; }
.theme-toggle:hover {
  color: var(--accent);
  border-color: var(--accent);
  transform: translateY(-2px);
}
.theme-toggle:active { transform: translateY(0) scale(.94); }

/* 汉堡按钮:默认隐藏(3 条 span) */
.nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 40px;
  height: 40px;
  padding: 0 9px;
  border: none;
  background: transparent;
  cursor: pointer;
}
.nav-toggle span {
  display: block;
  height: 1.8px;
  width: 100%;
  border-radius: 2px;
  background: var(--text);
  transition: transform .3s var(--ease), opacity .25s var(--ease);
}
/* 展开时变叉(aria-expanded=true 由 nav.js 设置) */
.nav-toggle[aria-expanded="true"] span:nth-child(1) { transform: translateY(6.8px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.nav-toggle[aria-expanded="true"] span:nth-child(3) { transform: translateY(-6.8px) rotate(-45deg); }

/* 无障碍:清晰聚焦描边 */
.logo:focus-visible,
.nav-links a:focus-visible,
.theme-toggle:focus-visible,
.nav-toggle:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 3px;
  border-radius: var(--r-sm);
}

/* ───── 移动端 ≤760px:汉堡 + 毛玻璃下拉面板竖排 ───── */
@media (max-width: 760px) {
  .nav-toggle { display: flex; }

  .nav-links {
    position: absolute;
    top: calc(100% + 1px);
    left: 0;
    right: 0;
    flex-direction: column;
    align-items: stretch;
    gap: 4px;
    padding: 10px 16px 16px;
    background: var(--nav-bg);
    -webkit-backdrop-filter: saturate(180%) blur(20px);
    backdrop-filter: saturate(180%) blur(20px);
    border-bottom: 1px solid var(--line);
    /* 默认收起 */
    opacity: 0;
    visibility: hidden;
    transform: translateY(-8px);
    pointer-events: none;
    transition: opacity .3s var(--ease), transform .3s var(--ease),
      visibility .3s var(--ease);
  }
  .nav-links.open {
    opacity: 1;
    visibility: visible;
    transform: none;
    pointer-events: auto;
  }
  .nav-links a {
    font-size: 16px;
    padding: 13px 6px;
    border-bottom: 1px solid var(--line-soft);
    color: var(--text);
  }
  .nav-links a::after { display: none; }
  .theme-toggle { align-self: flex-start; margin-top: 8px; }
}

@media (prefers-reduced-motion: reduce) {
  .theme-toggle:hover,
  .theme-toggle:active { transform: none; }
}