/* =================================================================
   header.css — sticky site header, nav, mobile menu
   ================================================================= */
.c-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--color-bg) 88%, transparent);
  backdrop-filter: saturate(140%) blur(10px);
  -webkit-backdrop-filter: saturate(140%) blur(10px);
  border-bottom: 1px solid transparent;
  transition:
    border-color var(--dur) var(--ease),
    background var(--dur) var(--ease);
}
/* subtle divider shown after scroll (toggled via .is-scrolled in JS) */
.c-header.is-scrolled {
  border-bottom-color: var(--color-line);
  background: color-mix(in srgb, var(--color-bg) 94%, transparent);
}

.c-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-md);
  min-height: 68px;
}

.c-brand {
  display: inline-flex;
  align-items: center;
  gap: 0.6rem;
  font-weight: var(--fw-semi);
  font-size: 1.0625rem;
  letter-spacing: -0.01em;
  color: var(--color-ink);
  white-space: nowrap;
}
.c-brand__mark {
  width: 30px;
  height: 30px;
  flex: 0 0 auto;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 9px;
  background: var(--color-accent);
  color: var(--color-on-accent);
  font-size: 0.85rem;
  font-weight: var(--fw-bold);
  letter-spacing: 0;
}

/* ---- Navigation ---- */
.c-nav {
  display: flex;
  align-items: center;
  gap: var(--space-lg);
}

.c-nav__list {
  display: flex;
  align-items: center;
  gap: clamp(0.75rem, 0.3rem + 1.4vw, 2rem);
}
.c-nav__link {
  position: relative;
  font-size: var(--fs-meta);
  font-weight: var(--fw-medium);
  color: var(--color-ink-soft);
  padding-block: 0.35rem;
  transition: color var(--dur) var(--ease);
}
.c-nav__link::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -2px;
  width: 100%;
  height: 1.5px;
  background: var(--color-accent);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--dur) var(--ease);
}
.c-nav__link:hover {
  color: var(--color-ink);
}
.c-nav__link:hover::after,
.c-nav__link.is-active::after {
  transform: scaleX(1);
}
.c-nav__link.is-active {
  color: var(--color-ink);
}

.c-nav__cta {
  margin-left: var(--space-xs);
}
.c-nav__cta .c-btn {
  white-space: nowrap;
}

/* ---- Hamburger (mobile) ---- */
.c-nav-toggle {
  display: inline-flex;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 44px;
  height: 44px;
  padding: 0 10px;
  background: transparent;
  border: 1px solid var(--color-line-strong);
  border-radius: var(--radius-sm);
  cursor: pointer;
}
.c-nav-toggle__bar {
  display: block;
  height: 2px;
  width: 100%;
  background: var(--color-ink);
  border-radius: 2px;
  transition:
    transform var(--dur) var(--ease),
    opacity var(--dur) var(--ease);
}
.c-nav-toggle[aria-expanded="true"] .c-nav-toggle__bar:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}
.c-nav-toggle[aria-expanded="true"] .c-nav-toggle__bar:nth-child(2) {
  opacity: 0;
}
.c-nav-toggle[aria-expanded="true"] .c-nav-toggle__bar:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

/* ---- Mobile: nav hidden until opened as a panel ---- */
@media (max-width: 47.99em) {
  .c-nav {
    position: fixed;
    inset: 68px 0 auto 0;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    background: var(--color-bg);
    border-bottom: 1px solid var(--color-line);
    padding: var(--space-sm) var(--gutter) var(--space-lg);
    box-shadow: var(--shadow-soft);
    transform: translateY(-12px);
    opacity: 0;
    visibility: hidden;
    transition:
      opacity var(--dur) var(--ease),
      transform var(--dur) var(--ease),
      visibility var(--dur);
  }
  .c-nav.is-open {
    transform: translateY(0);
    opacity: 1;
    visibility: visible;
  }
  .c-nav__list {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
  }
  .c-nav__link {
    padding: 0.9rem 0.25rem;
    font-size: 1.0625rem;
    border-bottom: 1px solid var(--color-line);
  }
  .c-nav__link::after {
    display: none;
  }
  .c-nav__cta {
    margin: var(--space-md) 0 0;
  }
  .c-nav__cta .c-btn {
    width: 100%;
  }
}

@media (min-width: 48em) {
  .c-nav-toggle {
    display: none;
  }
}