/* ──────────────────────────────────────────────────────────────────────────
   Research index page
   ────────────────────────────────────────────────────────────────────────── */

/* Nav — always opaque on research */
nav {
  position: fixed; top: 0; left: 0; right: 0;
  height: var(--nav-h);
  display: flex; align-items: center; justify-content: space-between;
  padding: 0 var(--section-pad-x);
  z-index: 300;
  background: rgba(251, 250, 247, .92);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: var(--border-light);
}

/* ──────────────────────────────────────────────────────────────────────────
   Page hero (dark)
   ────────────────────────────────────────────────────────────────────────── */
.page-hero {
  padding: calc(var(--nav-h) + var(--space-xl)) var(--section-pad-x) var(--space-lg);
  background: var(--dark-bg);
  position: relative; overflow: hidden;
}

.page-hero::after {
  content: '';
  position: absolute; inset: 0;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 512 512' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.75' numOctaves='4' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)' opacity='0.04'/%3E%3C/svg%3E");
  pointer-events: none; z-index: 0; opacity: .55;
}

.page-hero-inner {
  max-width: var(--container-max);
  margin: 0 auto;
  position: relative; z-index: 1;
  display: grid; grid-template-columns: 1fr 1fr;
  gap: var(--space-xl);
  align-items: end;
}

.page-hero-tag {
  display: inline-flex; align-items: center; gap: 8px;
  font-family: var(--font-sans);
  font-size: var(--text-label);
  font-weight: 600;
  letter-spacing: .14em; text-transform: uppercase;
  color: var(--peach);
  margin-bottom: var(--space-sm);
}

.page-hero-tag-dot {
  width: 6px; height: 6px; border-radius: 50%;
  background: var(--peach);
  animation: pulse 2.4s ease-in-out infinite;
}

.page-hero h1 {
  font-family: var(--font-serif);
  font-size: var(--text-display-xl);
  font-weight: 400; line-height: 1.06;
  letter-spacing: -.025em;
  color: var(--cream-on-dark);
  max-width: 14ch;
  text-wrap: balance;
}

.page-hero h1 em { font-style: italic; color: rgba(var(--cream-on-dark-rgb), .55); font-weight: 400; }

.page-hero-right {
  padding-bottom: 8px;
}

.page-hero-desc {
  font-family: var(--font-serif);
  font-size: var(--text-paragraph-m);
  font-weight: 300;
  line-height: 1.75;
  color: rgba(var(--cream-on-dark-rgb), .55);
  margin-bottom: var(--space-md);
  max-width: 44ch;
  text-wrap: pretty;
}

.page-hero-stats {
  display: flex; gap: var(--space-md);
}

.stat-val {
  font-family: var(--font-serif);
  font-size: 32px;
  font-weight: 400;
  color: var(--cream-on-dark);
  line-height: 1;
  margin-bottom: 6px;
}

.stat-label {
  font-family: var(--font-sans);
  font-size: var(--text-micro);
  font-weight: 600;
  letter-spacing: .12em; text-transform: uppercase;
  color: rgba(var(--cream-on-dark-rgb), .35);
}

/* ──────────────────────────────────────────────────────────────────────────
   Filter bar (sticky)
   ────────────────────────────────────────────────────────────────────────── */
.filter-bar {
  background: var(--cream-2);
  border-bottom: var(--border-hairline);
  padding: 0 var(--section-pad-x);
  position: sticky; top: var(--nav-h); z-index: 200;
}

.filter-bar-inner {
  max-width: var(--container-max);
  margin: 0 auto;
  display: flex; align-items: center; gap: 0;
  overflow-x: auto;
  scrollbar-width: none;
}

.filter-bar-inner::-webkit-scrollbar { display: none; }

.filter-btn {
  font-family: var(--font-sans);
  font-size: var(--text-cta);
  font-weight: 600;
  letter-spacing: .04em;
  color: var(--ink-44);
  background: none; border: none;
  padding: 18px 18px;
  cursor: pointer; white-space: nowrap;
  border-bottom: 2px solid transparent;
  transition: color var(--transition-fast),
              border-color var(--transition-fast);
}

.filter-btn:hover { color: var(--ink); }

.filter-btn.active { color: var(--ink); border-bottom-color: var(--ink); }

/* ──────────────────────────────────────────────────────────────────────────
   Search row
   ────────────────────────────────────────────────────────────────────────── */
.search-row {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: var(--space-md) var(--section-pad-x) 0;
  display: flex; gap: 12px; align-items: center;
}

.search-wrap {
  flex: 1; position: relative;
}

.search-icon {
  position: absolute; left: 16px; top: 50%;
  transform: translateY(-50%);
  width: 14px; height: 14px;
  color: var(--ink-44); pointer-events: none;
}

.search-input {
  width: 100%;
  background: var(--cream-2);
  border: 1px solid var(--ink-12);
  border-radius: var(--radius-pill);
  padding: 12px 14px 12px 40px;
  font-family: var(--font-serif);
  font-size: var(--text-paragraph-s);
  font-weight: 400;
  color: var(--ink);
  outline: none;
  transition: border-color var(--transition-fast);
}

.search-input::placeholder { color: var(--ink-44); }

.search-input:focus { border-color: var(--ink); }

.sort-select {
  background: var(--cream-2);
  border: 1px solid var(--ink-12);
  border-radius: var(--radius-pill);
  padding: 12px 16px;
  font-family: var(--font-sans);
  font-size: var(--text-cta);
  font-weight: 600;
  letter-spacing: .02em;
  color: var(--ink-60);
  outline: none;
  cursor: pointer; appearance: none;
  transition: border-color var(--transition-fast);
}

.sort-select:focus { border-color: var(--ink); }

/* ──────────────────────────────────────────────────────────────────────────
   Library layout
   ────────────────────────────────────────────────────────────────────────── */
.library-wrap {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: var(--space-lg) var(--section-pad-x) var(--space-2xl);
  display: grid;
  grid-template-columns: 1fr 280px;
  gap: var(--space-xl);
  align-items: start;
}

.post-list { display: flex; flex-direction: column; gap: 0; }

/* ──────────────────────────────────────────────────────────────────────────
   Featured paper (dark card)
   ────────────────────────────────────────────────────────────────────────── */
.post-featured {
  background: var(--dark-bg);
  border-radius: var(--radius-md);
  overflow: hidden;
  margin-bottom: var(--space-md);
  display: grid; grid-template-columns: 1fr 1fr;
  transition: transform var(--transition-fast);
  text-decoration: none;
}

.post-featured:hover { transform: translateY(-3px); }

.post-featured-body {
  padding: var(--space-md);
}

.post-featured-visual {
  background: linear-gradient(135deg, #1a1a1a 0%, var(--dark-bg) 60%);
  display: flex; align-items: center; justify-content: center;
  position: relative; overflow: hidden;
  min-height: 320px;
}

.post-featured-visual-inner {
  position: relative; z-index: 1;
  display: flex; flex-direction: column;
  align-items: center; gap: 16px;
}

.post-featured-badge {
  display: inline-flex; align-items: center; gap: 6px;
  font-family: var(--font-sans);
  font-size: var(--text-micro);
  font-weight: 700;
  letter-spacing: .14em; text-transform: uppercase;
  color: var(--blue-pale);
  background: rgba(var(--blue-rgb), .2);
  padding: 6px 12px; border-radius: var(--radius-pill);
  margin-bottom: var(--space-sm);
}

.post-featured-title {
  font-family: var(--font-serif);
  font-size: clamp(22px, 2.2vw, 28px);
  font-weight: 400; line-height: 1.2;
  color: var(--cream-on-dark);
  margin-bottom: 12px;
  text-wrap: balance;
}

.post-featured-excerpt {
  font-family: var(--font-serif);
  font-size: var(--text-paragraph-s);
  font-weight: 300;
  color: rgba(var(--cream-on-dark-rgb), .55);
  line-height: 1.75;
  margin-bottom: var(--space-md);
}

.post-featured-meta {
  display: flex; align-items: center; gap: 8px; flex-wrap: wrap;
}

.post-featured-date {
  font-family: var(--font-sans);
  font-size: var(--text-micro);
  font-weight: 600;
  letter-spacing: .12em; text-transform: uppercase;
  color: rgba(var(--cream-on-dark-rgb), .35);
}

.post-read-link {
  display: inline-flex; align-items: center; gap: 8px;
  font-family: var(--font-sans);
  font-size: var(--text-cta);
  font-weight: 700;
  letter-spacing: .04em;
  color: var(--cream-on-dark); text-decoration: none;
  margin-top: var(--space-sm); transition: gap var(--transition-fast);
}

.post-read-link:hover { gap: 12px; }

.post-read-link svg { width: 12px; height: 12px; }

.visual-grid {
  position: absolute; inset: 0;
  opacity: .12;
  background-image:
    linear-gradient(rgba(var(--blue-rgb), .5) 1px, transparent 1px),
    linear-gradient(90deg, rgba(var(--blue-rgb), .5) 1px, transparent 1px);
  background-size: 32px 32px;
}

.visual-chart {
  position: relative;
  width: 160px;
  opacity: .8;
}

/* ──────────────────────────────────────────────────────────────────────────
   Post cards (chronological list, ink-on-cream)
   ────────────────────────────────────────────────────────────────────────── */
.post-card {
  background: var(--cream-2);
  border: 1px solid var(--ink-08);
  border-radius: var(--radius-md);
  padding: var(--space-md);
  display: flex; gap: var(--space-md);
  align-items: flex-start;
  text-decoration: none; color: inherit;
  transition: transform var(--transition-fast),
              border-color var(--transition-fast),
              background var(--transition-fast);
  margin-bottom: 12px;
}

.post-card:hover {
  transform: translateY(-2px);
  border-color: var(--ink);
  background: #fff;
}

.post-card-num {
  font-family: var(--font-serif);
  font-size: 44px;
  font-weight: 300;
  line-height: 1;
  color: var(--ink-12);
  flex-shrink: 0;
  width: 48px; text-align: right;
  margin-top: -4px;
  user-select: none;
}

.post-card-body { flex: 1; min-width: 0; }

.post-card-tags {
  display: flex; flex-wrap: wrap; gap: 6px;
  margin-bottom: 12px;
}

.post-card-title {
  font-family: var(--font-serif);
  font-size: var(--text-display-s);
  font-weight: 500;
  line-height: 1.25;
  color: var(--ink);
  margin-bottom: 8px;
  text-wrap: balance;
}

.post-card-excerpt {
  font-family: var(--font-serif);
  font-size: var(--text-paragraph-s);
  font-weight: 300;
  color: var(--ink-60);
  line-height: 1.7;
  margin-bottom: 14px;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.post-card-foot {
  display: flex; align-items: center; gap: 16px;
}

.post-card-date,
.post-card-read {
  font-family: var(--font-sans);
  font-size: var(--text-micro);
  font-weight: 600;
  letter-spacing: .12em; text-transform: uppercase;
  color: var(--ink-44);
}

.post-card-arrow {
  margin-left: auto; flex-shrink: 0;
  color: var(--ink-44);
  transition: transform var(--transition-fast),
              color var(--transition-fast);
}

.post-card:hover .post-card-arrow { transform: translateX(4px); color: var(--ink); }

/* Post tags are defined in css_shared.css.
   Filled accent backgrounds + ink text read fine on both light and dark
   contexts (post hero, featured card) — no per-context override needed. */

/* Upcoming card state */
.post-card.is-upcoming { opacity: .9; }
.post-card.is-upcoming .post-card-arrow { display: none; }

.post-tag-upcoming {
  font-family: var(--font-sans);
  font-size: var(--text-micro);
  font-weight: 700;
  letter-spacing: .08em; text-transform: uppercase;
  padding: 4px 10px; border-radius: var(--radius-pill);
  background: var(--ink);
  color: var(--cream-on-dark);
}

/* ──────────────────────────────────────────────────────────────────────────
   Sidebar
   ────────────────────────────────────────────────────────────────────────── */
.sidebar { display: flex; flex-direction: column; gap: var(--space-md); }

.sidebar-block {
  background: var(--cream-2);
  border: 1px solid var(--ink-08);
  border-radius: var(--radius-md);
  padding: var(--space-md);
}

.sidebar-title {
  font-family: var(--font-sans);
  font-size: var(--text-micro);
  font-weight: 700;
  letter-spacing: .12em; text-transform: uppercase;
  color: var(--ink-44);
  margin-bottom: var(--space-sm);
  display: flex; align-items: center; gap: 8px;
}

.sidebar-title::before {
  content: '';
  display: block; width: 14px; height: 1.5px;
  background: var(--ink);
}

.archive-list { display: flex; flex-direction: column; gap: 0; }

.archive-item {
  display: flex; justify-content: space-between; align-items: center;
  padding: 10px 0;
  border-bottom: 1px solid var(--ink-08);
  cursor: pointer;
  transition: color var(--transition-fast);
}

.archive-item:last-child { border-bottom: none; }

.archive-item:hover .archive-month { color: var(--ink); }

.archive-month {
  font-family: var(--font-serif);
  font-size: var(--text-paragraph-s);
  font-weight: 400;
  color: var(--ink-60);
  transition: color var(--transition-fast);
}

.archive-count {
  font-family: var(--font-sans);
  font-size: var(--text-micro);
  font-weight: 700;
  letter-spacing: .06em;
  color: var(--ink-44);
  background: var(--cream);
  padding: 2px 10px; border-radius: var(--radius-pill);
}

.tag-cloud { display: flex; flex-wrap: wrap; gap: 6px; }

.tag-cloud-item {
  font-family: var(--font-sans);
  font-size: var(--text-micro);
  font-weight: 700;
  letter-spacing: .08em; text-transform: uppercase;
  color: var(--ink);
  background: var(--cream);
  border: 1px solid var(--ink-12);
  padding: 5px 10px; border-radius: var(--radius-pill);
  cursor: pointer;
  transition: transform var(--transition-fast),
              box-shadow var(--transition-fast),
              background var(--transition-fast),
              color var(--transition-fast),
              border-color var(--transition-fast);
}

/* Colored variants — fills mirror the .post-tag chip cycle */
.tag-cloud-item.tag-ai   { background: var(--rust);  border-color: transparent; }
.tag-cloud-item.tag-econ { background: var(--blue);  border-color: transparent; }
.tag-cloud-item.tag-math { background: var(--peach); border-color: transparent; }
.tag-cloud-item.tag-qfin { background: var(--green); border-color: transparent; }

/* Hover: slight lift across the board */
.tag-cloud-item:hover { transform: translateY(-1px); }

/* Active state */
/*  - "All" (no tag-* class) shifts to ink fill, as before */
/*  - Colored chips keep their fill; gain an ink outline as the "selected" cue */
.tag-cloud-item.active {
  outline: 2px solid var(--ink);
  outline-offset: 2px;
}
.tag-cloud-item[data-tag="all"]:hover,
.tag-cloud-item[data-tag="all"].active {
  background: var(--ink); color: var(--cream-on-dark); border-color: var(--ink);
  outline: none;
}

.newsletter-block {
  background: var(--dark-bg);
  border-radius: var(--radius-md);
  padding: var(--space-md);
}

.newsletter-block .sidebar-title { color: rgba(var(--cream-on-dark-rgb), .35); }

.newsletter-desc {
  font-family: var(--font-serif);
  font-size: var(--text-paragraph-s);
  font-weight: 300;
  color: rgba(var(--cream-on-dark-rgb), .55);
  line-height: 1.7;
  margin-bottom: var(--space-sm);
}

.newsletter-input {
  width: 100%;
  background: rgba(var(--cream-on-dark-rgb), .06);
  border: 1px solid rgba(var(--cream-on-dark-rgb), .12);
  border-radius: var(--radius-pill);
  padding: 12px 16px;
  font-family: var(--font-serif);
  font-size: var(--text-paragraph-s);
  font-weight: 400;
  color: var(--cream-on-dark);
  outline: none;
  transition: border-color var(--transition-fast);
  margin-bottom: 10px;
}

.newsletter-input::placeholder { color: rgba(var(--cream-on-dark-rgb), .35); }

.newsletter-input:focus { border-color: var(--cream-on-dark); }

.newsletter-btn {
  width: 100%;
  background: var(--cream-on-dark); color: var(--ink);
  border: none; border-radius: var(--radius-pill);
  padding: 12px 20px;
  font-family: var(--font-sans);
  font-size: var(--text-cta);
  font-weight: 700;
  letter-spacing: .04em;
  cursor: pointer;
  transition: background var(--transition-fast),
              transform var(--transition-fast);
}

.newsletter-btn:hover { background: #fff; transform: translateY(-1px); }

.newsletter-btn:disabled { opacity: .6; cursor: default; transform: none; }

/* Dark-context status: success reads on the near-black panel; error stays rust */
.form-status--dark { margin-top: 4px; }
.form-status--dark.is-success { color: var(--cream-on-dark); }
.form-status--dark.is-error   { color: var(--rust); }

/* ──────────────────────────────────────────────────────────────────────────
   Pagination
   ────────────────────────────────────────────────────────────────────────── */
.pagination {
  display: flex; align-items: center; gap: 8px;
  margin-top: var(--space-md);
}

.page-btn {
  width: 40px; height: 40px; border-radius: var(--radius-pill);
  display: flex; align-items: center; justify-content: center;
  font-family: var(--font-sans);
  font-size: var(--text-cta);
  font-weight: 600;
  color: var(--ink-60);
  background: var(--cream-2);
  border: 1px solid var(--ink-12);
  cursor: pointer;
  transition: all var(--transition-fast);
}

.page-btn:hover { border-color: var(--ink); color: var(--ink); }

.page-btn.active { background: var(--ink); color: var(--cream-on-dark); border-color: var(--ink); }

.page-btn-nav {
  width: auto; padding: 0 16px;
  font-size: var(--text-micro);
  letter-spacing: .04em;
}

/* ──────────────────────────────────────────────────────────────────────────
   Empty state
   ────────────────────────────────────────────────────────────────────────── */
.empty-state {
  padding: var(--space-xl) 0; text-align: center;
  display: none;
}

.empty-state h3 {
  font-family: var(--font-serif);
  font-size: var(--text-display-m);
  font-weight: 500;
  color: var(--ink);
  margin-bottom: 10px;
}

.empty-state p {
  font-family: var(--font-serif);
  font-size: var(--text-paragraph-s);
  color: var(--ink-44);
}

/* ──────────────────────────────────────────────────────────────────────────
   Mobile
   ────────────────────────────────────────────────────────────────────────── */
@media (max-width: 960px) {
  .page-hero-inner { grid-template-columns: 1fr; gap: var(--space-md); }
  .library-wrap { grid-template-columns: 1fr; gap: var(--space-md); }
  .sidebar { order: -1; }
  .post-featured { grid-template-columns: 1fr; }
  .post-featured-visual { min-height: 180px; }
}