/* =====================================================================
   layout.css — Navigation, page sections, responsive grid/flex
   ===================================================================== */

/* ---- Navigation ---- */
#navbar {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 1000;
  height: var(--nav-height);
  display: flex;
  align-items: center;
  padding: 0 var(--space-xl);
  transition: background var(--transition-mid), box-shadow var(--transition-mid);
}

#navbar.scrolled {
  background: rgba(2, 4, 8, 0.92);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  box-shadow: 0 2px 24px rgba(0, 212, 255, 0.08);
  border-bottom: 1px solid var(--color-border);
}

.nav-inner {
  max-width: var(--max-width);
  width: 100%;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-xl);
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  text-decoration: none;
  flex-shrink: 0;
}
.nav-logo-text {
  font-size: var(--font-size-lg);
  font-weight: 700;
  color: var(--color-text);
  white-space: nowrap;
}
.nav-logo-sub {
  font-size: var(--font-size-xs);
  color: var(--color-text-muted);
  letter-spacing: 0.05em;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: var(--space-xs);
}

.nav-link {
  position: relative;
  padding: var(--space-sm) var(--space-md);
  font-size: var(--font-size-sm);
  font-weight: 500;
  color: var(--color-text-muted);
  border-radius: var(--radius-sm);
  transition: color var(--transition-fast), background var(--transition-fast);
  white-space: nowrap;
  cursor: pointer;
  text-decoration: none;
  user-select: none;
}
.nav-link:hover {
  color: var(--color-cyan);
  background: rgba(0, 212, 255, 0.06);
}
.nav-link.active {
  color: var(--color-cyan);
}
.nav-link.active::after {
  content: '';
  position: absolute;
  bottom: 4px; left: 50%;
  transform: translateX(-50%);
  width: 16px; height: 2px;
  background: var(--color-cyan);
  border-radius: var(--radius-full);
}

/* Language switcher */
.lang-switcher {
  display: flex;
  align-items: center;
  gap: 2px;
  background: rgba(255,255,255,0.05);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-full);
  padding: 3px;
  flex-shrink: 0;
}
.lang-btn {
  padding: 0.25rem 0.65rem;
  border-radius: var(--radius-full);
  font-size: 0.75rem;
  font-weight: 700;
  color: var(--color-text-muted);
  cursor: pointer;
  background: none;
  border: none;
  transition: background var(--transition-fast), color var(--transition-fast);
  letter-spacing: 0.03em;
  line-height: 1.6;
}
.lang-btn:hover { color: var(--color-cyan); }
.lang-btn.active {
  background: var(--grad-primary);
  color: #fff;
}

/* Hamburger */
.nav-hamburger {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 36px; height: 36px;
  padding: 4px;
  cursor: pointer;
  background: none;
  border: none;
}
.nav-hamburger span {
  display: block;
  height: 2px;
  background: var(--color-text);
  border-radius: var(--radius-full);
  transition: transform var(--transition-mid), opacity var(--transition-mid), width var(--transition-mid);
}
.nav-hamburger.open span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-hamburger.open span:nth-child(2) { opacity: 0; width: 0; }
.nav-hamburger.open span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* Mobile nav overlay */
.nav-mobile {
  display: none;
  position: fixed;
  top: var(--nav-height); left: 0; right: 0;
  background: rgba(2, 4, 8, 0.97);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--color-border);
  z-index: 999;
  padding: var(--space-md) var(--space-xl) var(--space-xl);
  flex-direction: column;
  gap: var(--space-xs);
}
.nav-mobile.open { display: flex; }
.nav-mobile .nav-link {
  padding: var(--space-md);
  font-size: var(--font-size-md);
  border-radius: var(--radius-md);
}

/* ---- Page sections ---- */
.page-section {
  display: none;
  min-height: 100vh;
  padding-top: var(--nav-height);
}
.page-section.active { display: block; }

/* ---- Section wrapper ---- */
.section-block {
  padding: var(--space-4xl) 0;
}

/* ---- 2-col grid ---- */
.grid-2 {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-2xl);
  align-items: start;
}

/* ---- 3-col grid ---- */
.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-xl);
}

/* ---- 4-col grid (2×2 on desktop) ---- */
.grid-4 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--space-xl);
}

/* ---- Full-span grid child ---- */
.span-full { grid-column: 1 / -1; }

/* ---- Responsive ---- */
@media (max-width: 1024px) {
  .grid-3 { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 768px) {
  :root { --nav-height: 64px; }

  h1 { font-size: var(--font-size-4xl); }
  h2 { font-size: var(--font-size-3xl); }

  .container { padding: 0 var(--space-md); }

  #navbar { padding: 0 var(--space-md); }

  .nav-links { display: none; }
  .nav-hamburger { display: flex; }

  .grid-2 { grid-template-columns: 1fr; gap: var(--space-xl); }
  .grid-3 { grid-template-columns: 1fr; }
  .grid-4 { grid-template-columns: 1fr; }

  .section-block { padding: var(--space-2xl) 0; }

  .section-title { font-size: var(--font-size-3xl); }
}

@media (min-width: 769px) and (max-width: 1024px) {
  .grid-4 { grid-template-columns: repeat(2, 1fr); }
}