/* ─────────────────────────────────────────────────────────────
   Case Studies — light editorial section on the dark site shell.
   Builds on assets/site.css. All colours derive from the brand set.
   ───────────────────────────────────────────────────────────── */

:root{
  /* --sig-ink (brand green darkened for light surfaces) lives in site.css */
  --l-base:  #E5E5E5;   /* brand neutral light — section floor */
  --l-card:  #FFFFFF;   /* brand white — elevated card */
  --l-rule:  rgba(17,17,17,.13);
  --l-rule-strong: rgba(17,17,17,.26);
  --l-body:  #6D6F73;   /* brand grey — 4.9:1 on white */
}

/* ── Light section shell ──────────────────────────────────── */
.light-zone{
  background:var(--l-base);
  color:var(--ink);
}
.light-zone .tag{ color:#5C5E62; }
.light-zone .eyebrow{ color:var(--sig-ink); }
.light-zone .rule{ background:var(--l-rule); }

/* ── Filter bar ───────────────────────────────────────────── */
.filter-bar{
  display:flex; flex-wrap:wrap; gap:.5rem;
}
.filter-btn{
  font-family:"Space Grotesk", sans-serif;
  font-size:.8125rem; font-weight:500;
  letter-spacing:-.01em;
  padding:.6rem 1.1rem;
  border:1px solid var(--l-rule-strong);
  background:transparent;
  color:var(--ink);
  cursor:pointer;
  transition:background-color .35s var(--ease-out), color .35s var(--ease-out),
             border-color .35s var(--ease-out), transform .35s var(--ease-spring);
}
.filter-btn:hover{ border-color:var(--ink); transform:translateY(-1px); }
.filter-btn:focus-visible{ outline:2px solid var(--sig-ink); outline-offset:3px; }
.filter-btn[aria-pressed="true"]{
  background:var(--ink); color:#FFFFFF; border-color:var(--ink);
}
.filter-btn .n{
  font-family:"IBM Plex Mono", monospace;
  font-size:.6875rem;
  opacity:.55;
  margin-left:.45rem;
}

/* ── Case study card ──────────────────────────────────────── */
.cs-card{
  position:relative;
  background:var(--l-card);
  border:1px solid var(--l-rule);
  transition:border-color .5s var(--ease-out), box-shadow .5s var(--ease-out),
             transform .5s var(--ease-spring), opacity .4s var(--ease-out);
}
.cs-card:hover{
  border-color:var(--l-rule-strong);
  transform:translateY(-2px);
  box-shadow:0 24px 48px -32px rgba(17,17,17,.4);
}
/* registration marks, inverted for light */
.cs-card::before,
.cs-card::after{
  content:'';
  position:absolute;
  width:11px; height:11px;
  border:1px solid var(--sig-ink);
  opacity:0;
  transition:opacity .45s var(--ease-out), transform .45s var(--ease-spring);
  pointer-events:none;
}
.cs-card::before{ top:-1px; left:-1px; border-right:0; border-bottom:0; transform:translate(4px,4px); }
.cs-card::after{ bottom:-1px; right:-1px; border-left:0; border-top:0; transform:translate(-4px,-4px); }
.cs-card:hover::before,
.cs-card:hover::after{ opacity:1; transform:translate(0,0); }

.cs-card[hidden]{ display:none; }

.cs-index{
  font-family:"Space Grotesk", sans-serif;
  font-weight:700;
  font-size:clamp(2.5rem,6vw,3.75rem);
  line-height:.8;
  letter-spacing:-.05em;
  color:transparent;
  -webkit-text-stroke:1px rgba(17,17,17,.38);
  user-select:none;
}

.cs-sector{
  font-family:"IBM Plex Mono", monospace;
  font-size:.6875rem;
  letter-spacing:.08em;
  text-transform:uppercase;
  color:var(--sig-ink);
}

.cs-body{ color:var(--l-body); }

/* Metric strip inside a card */
.cs-metrics{
  display:grid;
  grid-template-columns:repeat(3,1fr);
  gap:1px;
  background:var(--l-rule);
  border:1px solid var(--l-rule);
}
.cs-metrics > div{ background:var(--l-card); padding:1rem 1.1rem; }

/* Embedded dark instrument panel — the one dark element in the card */
.cs-scope{
  background:var(--surface-base);
  border:1px solid rgba(17,17,17,.9);
  padding:1.1rem;
}
.cs-scope .lbl{
  font-family:"IBM Plex Mono", monospace;
  font-size:.625rem;
  letter-spacing:.1em;
  text-transform:uppercase;
  color:var(--tag-ink);
}

/* ── Read more disclosure ─────────────────────────────────── */
.cs-more{
  display:grid;
  grid-template-rows:0fr;
  transition:grid-template-rows .6s var(--ease-spring);
}
.cs-more > div{ overflow:hidden; }
.cs-more.open{ grid-template-rows:1fr; }

.cs-toggle{
  display:inline-flex; align-items:center; gap:.6rem;
  font-family:"Space Grotesk", sans-serif;
  font-size:.875rem; font-weight:600;
  padding:.8rem 1.4rem;
  border:1px solid var(--ink);
  background:transparent;
  color:var(--ink);
  cursor:pointer;
  transition:background-color .35s var(--ease-out), color .35s var(--ease-out),
             transform .35s var(--ease-spring);
}
.cs-toggle:hover{ background:var(--ink); color:#FFFFFF; transform:translateY(-2px); }
.cs-toggle:active{ transform:translateY(0) scale(.99); }
.cs-toggle:focus-visible{ outline:2px solid var(--sig-ink); outline-offset:3px; }
.cs-toggle .chev{ transition:transform .45s var(--ease-spring); }
.cs-toggle[aria-expanded="true"] .chev{ transform:rotate(180deg); }

/* Detail blocks revealed by Read more */
.cs-detail h4{
  font-family:"Space Grotesk", sans-serif;
  font-size:.6875rem; font-weight:600;
  letter-spacing:.14em; text-transform:uppercase;
  color:var(--sig-ink);
}
.cs-detail p{ color:var(--l-body); }
.cs-detail li{
  display:flex; gap:.75rem;
  padding:.55rem 0;
  color:var(--l-body);
  font-size:.875rem;
  line-height:1.65;
}
.cs-detail li::before{
  content:'';
  width:5px; height:5px; margin-top:.6rem;
  background:var(--sig-ink);
  flex:none;
}

/* Technology chips */
.chip{
  display:inline-block;
  font-family:"IBM Plex Mono", monospace;
  font-size:.6875rem;
  letter-spacing:.04em;
  padding:.34rem .7rem;
  border:1px solid var(--l-rule-strong);
  color:#4A4C50;
}

/* ── Empty state for filters ──────────────────────────────── */
#csEmpty{ display:none; }
#csEmpty.show{ display:block; }

@media (prefers-reduced-motion: reduce){
  .cs-card,.cs-toggle,.filter-btn,.cs-more{ transition:none !important; }
}