/* =========================
   HEADER (Shared)
========================= */
.header{
  position: sticky;
  top: 0;
  z-index: 999;
  background: #00629b;
  transition: background .35s ease, box-shadow .35s ease, backdrop-filter .35s ease;
  box-shadow: 0 2px 5px rgba(0,0,0,0.10);
}

.nav{
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 25px;
  padding: 15px;
  flex-wrap: wrap;
}

/* links */
.nav a{
  color: #fff;
  text-decoration: none;
  font-weight: 600;
  position: relative;
  transition: opacity .2s ease;
}

.nav a:hover{ opacity: .85; }

/* underline hover */
.nav a::after{
  content:"";
  position:absolute;
  left:0;
  bottom:-6px;
  width:0;
  height:2px;
  background:#fff;
  transition: width .25s ease;
}
.nav a:hover::after{ width:100%; }

/* active link underline */
.nav a.active::after{
  width:100%;
}

/* ===== Scroll effect (supports is-scrolled OR scrolled) ===== */
.header.is-scrolled,
.header.scrolled{
  background: rgba(255,255,255,0.92);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  box-shadow: 0 10px 30px rgba(0,0,0,0.12);
}

.header.is-scrolled .nav a,
.header.scrolled .nav a{
  color:#0b2a3a;
}
.header.is-scrolled .nav a::after,
.header.scrolled .nav a::after{
  background:#0b2a3a;
}

/* ===== Dark Theme ===== */
html[data-theme="dark"] .header{
  background: rgba(6, 30, 52, 0.45);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  box-shadow: none;
}

html[data-theme="dark"] .nav a::after{
  background:#0099cc;
}

html[data-theme="dark"] .header.is-scrolled,
html[data-theme="dark"] .header.scrolled{
  background: rgba(6, 30, 52, 0.60);
  box-shadow: 0 10px 30px rgba(0,0,0,0.35);
}

html[data-theme="dark"] .header.is-scrolled .nav a,
html[data-theme="dark"] .header.scrolled .nav a{
  color:#fff;
}
html[data-theme="dark"] .header.is-scrolled .nav a::after,
html[data-theme="dark"] .header.scrolled .nav a::after{
  background:#0099cc;
}

/* theme toggle button spacing inside nav */
.nav .theme-toggle{
  margin-left: 10px;
}