/* ------------------------------------------------------------------
   Fixed top bar: brand, nav, theme / language / menu buttons.
   ------------------------------------------------------------------ */

header{
  position:fixed; top:0; left:0; right:0; z-index:100;
  display:flex; align-items:center; justify-content:space-between; gap:16px;
  padding:14px clamp(18px,4vw,44px);
  border-bottom:1px solid transparent; background:transparent;
  transition:background .4s var(--ease), border-color .4s var(--ease), padding .4s var(--ease);
  transform:translateZ(0); /* own compositor layer — keeps it stable while the page repaints */
}
header.scrolled{
  background:color-mix(in srgb,var(--bg) 92%,transparent);
  backdrop-filter:blur(10px); -webkit-backdrop-filter:blur(10px);
  border-bottom-color:var(--border); padding-top:10px; padding-bottom:10px;
}
.brand{display:flex; align-items:center; gap:10px; font-family:var(--font-display); font-weight:700; letter-spacing:-.03em; font-size:1.02rem}
.brand .dot{width:9px; height:9px; border-radius:50%; background:var(--accent); box-shadow:0 0 14px var(--accent); transition:background .8s var(--ease), box-shadow .8s var(--ease)}
.brand .fm{font-family:var(--font-mono); font-size:.7rem; color:var(--text-3); font-weight:400; letter-spacing:.12em; border:1px solid var(--border); border-radius:5px; padding:2px 6px}
nav{display:flex; align-items:center; gap:4px}
nav a{
  display:flex; align-items:center; gap:8px; padding:8px 14px; border-radius:999px; font-size:.88rem;
  color:var(--text-2); font-weight:500; transition:color .3s var(--ease), background .3s var(--ease);
}
nav a .n{font-family:var(--font-mono); font-size:.68rem; color:var(--text-3); transition:color .3s var(--ease)}
nav a:hover,nav a.active{color:var(--text); background:var(--surface-2)}
nav a.active .n{color:var(--accent)}
.nav-tools{display:flex; align-items:center; gap:8px}
.icon-btn{
  width:38px; height:38px; display:grid; place-items:center;
  border:1px solid var(--border); border-radius:12px; background:var(--surface);
  transition:all .3s var(--ease);
}
.icon-btn:hover{border-color:var(--border-2); background:var(--surface-2); transform:translateY(-1px)}
.icon-btn svg{width:18px; height:18px}
.lang-btn{width:auto; gap:6px; padding:0 11px; display:flex; align-items:center; font-family:var(--font-display); font-size:.76rem; font-weight:700; letter-spacing:.06em}
.lang-btn svg{width:16px; height:16px; opacity:.8}
html[data-theme="dark"] .i-sun{display:block} html[data-theme="dark"] .i-moon{display:none}
html[data-theme="light"] .i-sun{display:none} html[data-theme="light"] .i-moon{display:block}
.menu-btn{display:none}
@media(max-width:880px){
  nav{
    position:fixed; inset:0 0 auto 0; top:0; flex-direction:column; align-items:stretch;
    padding:88px 22px 26px; gap:4px; background:var(--bg);
    border-bottom:1px solid var(--border);
    transform:translateY(-110%); transition:transform .45s var(--ease); z-index:-1;
  }
  nav.open{transform:translateY(0)}
  nav a{padding:14px 16px; font-size:1.05rem}
  .menu-btn{display:grid}
}