/* Shared navigation, back-to-top, reading progress. Linked by index + edition. */
.skip{position:absolute;left:-999px;top:8px;z-index:200;background:var(--text,#f3f4f6);color:#0a0b0f;padding:8px 14px;border-radius:8px;font-family:var(--mono);font-size:13px}
.skip:focus{left:12px}
.nav{position:sticky;top:0;z-index:100;transition:background .25s ease,border-color .25s ease,backdrop-filter .25s ease;border-bottom:1px solid transparent}
.nav.is-scrolled{background:color-mix(in srgb,#0a0b0f 78%,transparent);backdrop-filter:blur(14px) saturate(1.2);-webkit-backdrop-filter:blur(14px) saturate(1.2);border-bottom-color:var(--border,#23262f)}
.nav__in{max-width:var(--maxw,1160px);margin:0 auto;padding:12px 24px;display:flex;align-items:center;gap:18px}
.nav__brand{display:inline-flex;align-items:center;gap:10px;flex:none}
.nav__mark{width:30px;height:30px;display:grid;place-items:center;border-radius:9px;color:#0a0b0f;background:linear-gradient(135deg,#7c9cff,#5ed3a8)}
.nav__mark svg{width:17px;height:17px}
.nav__brandtx{font-family:var(--serif,Georgia,serif);font-weight:500;font-size:17px;letter-spacing:-.01em;color:var(--text,#f3f4f6)}
.nav__links{display:flex;align-items:center;gap:4px;margin-left:6px}
.nav__link{font-family:var(--mono,monospace);font-size:13px;color:var(--text-dim,#9aa0ac);padding:7px 12px;border-radius:99px;transition:color .2s,background .2s}
.nav__link:hover{color:var(--text,#f3f4f6);background:color-mix(in srgb,#fff 6%,transparent)}
.nav__link.is-active{color:var(--text,#f3f4f6);background:color-mix(in srgb,var(--accent,#7c9cff) 16%,transparent)}
.nav__cta{margin-left:auto;display:inline-flex;align-items:center;gap:7px;font-family:var(--mono,monospace);font-size:13px;color:#0a0b0f;background:var(--text,#f3f4f6);border-radius:99px;padding:9px 16px;white-space:nowrap;transition:transform .2s var(--ease,ease),opacity .2s}
.nav__cta:hover{transform:translateY(-1px);opacity:.92;color:#0a0b0f}
.nav__cta .arw{width:12px;height:12px}
.backtop{position:fixed;right:22px;bottom:22px;z-index:90;width:44px;height:44px;display:grid;place-items:center;border-radius:50%;border:1px solid var(--border,#23262f);background:color-mix(in srgb,#14161d 88%,transparent);backdrop-filter:blur(8px);color:var(--text,#f3f4f6);cursor:pointer;opacity:0;transform:translateY(8px);pointer-events:none;transition:opacity .25s,transform .25s}
.backtop.is-on{opacity:1;transform:none;pointer-events:auto}
.backtop:hover{border-color:var(--accent,#7c9cff);color:var(--accent,#7c9cff)}
.backtop svg{width:19px;height:19px}
@media(max-width:680px){
  .nav__brandtx{display:none}
  .nav__cta{display:none}
  .nav__links{margin-left:auto;gap:2px}
  .nav__link{padding:7px 9px;font-size:12px}
}