.masthead { border-bottom: 1px solid var(--line); background: var(--space); position: relative; z-index: 5; }
.masthead__inner { display: flex; align-items: center; justify-content: space-between; gap: 2rem; padding-block: 1.5rem; }
.masthead__brand { display: flex; align-items: center; gap: 1rem; color: var(--ink); text-decoration: none; min-height: 48px; font-size: 1rem; }
.masthead__brand:hover { color: var(--ink); }
.masthead__symbol { position: relative; flex-shrink: 0; width: 36px; height: 36px; border: 1px solid var(--cyan); border-radius: 50%; }
.masthead__symbol::before { content: ""; position: absolute; inset: 7px; border: 1px solid var(--teal); border-radius: 50%; }
.masthead__symbol::after { content: ""; position: absolute; width: 5px; height: 5px; left: 15px; top: 15px; border-radius: 50%; background: var(--mint); box-shadow: 0 0 12px #00ff8855; }
.masthead__name { display: block; font-family: var(--editorial); font-size: 1.125rem; line-height: 1.35; font-weight: 600; }
.masthead__subline { display: block; color: var(--muted); font-size: 1rem; line-height: 1.5; }
.topic-nav { display: flex; flex-wrap: wrap; gap: .5rem; }
.topic-nav__cluster { position: relative; }
.topic-nav__heading { list-style: none; display: flex; align-items: center; gap: 1rem; padding: .625rem 1rem; min-height: 44px; border: 1px solid transparent; border-radius: 8px; cursor: pointer; color: var(--ink); font-size: 1rem; }
.topic-nav__heading::-webkit-details-marker { display: none; }
.topic-nav__heading::after { content: "+"; font-family: var(--data); font-size: 1rem; color: var(--cyan); }
.topic-nav__cluster[open] .topic-nav__heading { background: var(--panel); border-color: var(--line); }
.topic-nav__cluster[open] .topic-nav__heading::after { content: "−"; }
.topic-nav__items { position: absolute; top: calc(100% + .5rem); right: 0; width: 288px; margin: 0; padding: .5rem; list-style: none; border: 1px solid var(--line); border-radius: 8px; background: var(--surface); box-shadow: 0 16px 40px #0005; }
.topic-nav__items li { padding: 0; margin: 0; }
.topic-nav__link { display: flex; align-items: center; min-height: 48px; padding: .625rem .75rem; border-radius: 4px; color: var(--ink); font-size: 1rem; text-decoration: none; }
.topic-nav__link:hover, .topic-nav__link[aria-current="page"] { color: var(--cyan); background: var(--panel); }
.topic-nav__link[aria-current="page"] { border-left: 2px solid var(--cyan); padding-left: calc(.75rem - 2px); }

@media (max-width: 760px) {
  .masthead__inner { display: block; padding-block: 1rem; }
  .topic-nav { margin-top: 1rem; gap: 0 .25rem; }
  .topic-nav__heading { padding-inline: .5rem; gap: .5rem; }
  .topic-nav__cluster { position: static; }
  .topic-nav__items { left: 1.5rem; right: 1.5rem; width: auto; top: 100%; }
}

@media (max-width: 360px) {
  .topic-nav { display: grid; grid-template-columns: minmax(0, 1fr); }
  .topic-nav__heading { justify-content: space-between; }
}