/* =========================================================================
   The Periodic Table Room — per-element room pages (docs/rooms/*.html)
   Loaded on top of style.css (shared HUD / panel / XR / fps look).
   ========================================================================= */

/* ---------- Back link (exit the element room) ---------- */
#back {
  position: fixed; top: 26px; right: 26px; z-index: 20;
  font-family: var(--mono); font-size: 12.5px; letter-spacing: .03em;
  color: var(--text); text-decoration: none;
  padding: 9px 14px; border-radius: 12px;
  border: 1px solid var(--panel-border);
  background: var(--panel); backdrop-filter: blur(8px);
  transition: border-color .18s ease, box-shadow .18s ease, transform .18s ease;
  display: inline-flex; align-items: center; gap: 6px;
}
#back:hover {
  border-color: rgba(63,224,255,.55);
  box-shadow: 0 0 0 3px rgba(63,224,255,.12);
  transform: translateY(-1px);
}

/* ---------- Element symbol in the HUD title ---------- */
#hud h1 { display: flex; align-items: center; gap: 10px; }
#hud .room-symbol {
  font-family: var(--mono); font-weight: 700;
  min-width: 46px; text-align: center;
  padding: 2px 6px; border-radius: 8px;
  border: 1px solid currentColor; background: rgba(0,0,0,.35);
  -webkit-text-fill-color: currentColor;
}

/* On mobile the #fps counter and #back could overlap the title; tuck them. */
@media (max-width: 720px) {
  #hud { top: 12px; left: 12px; max-width: 62vw; }
  #back { top: 12px; right: 12px; }
}

#panel-body .learn-block { margin-top: 10px; display: grid; gap: 6px; }
#panel-body .learn-line { font-size: 12px; color: var(--muted); line-height: 1.45; margin: 0; }
#panel-body .learn-tag { font-weight: 700; letter-spacing: 0.08em; margin-right: 6px; font-size: 10px; }