/* ==========================================================================
   shared.css — Problem Archive
   Plain black-and-white academic theme. No frameworks.
   Used by index.html (library) and optionally by papers/*.html.
   Papers in /papers/ are fully standalone (embedded styles) so this file
   is NOT required for them to render. It is the single stylesheet for the
   homepage / archive chrome.
   All paths that reference this file must be relative (GitHub Pages subpath
   safe). e.g. from index.html:  assets/css/shared.css
              from papers/x.html: ../assets/css/shared.css (optional)
   ========================================================================== */

:root {
  --ink: #111;
  --paper: #fff;
  --muted: #555;
  --rule: #111;
  --hairline: #ccc;
  --focus: #000;
  --max-width: 44rem;
  --serif: "Latin Modern Roman", "Computer Modern", "CMU Serif",
           "STIX Two Text", "TeX Gyre Termes", "Times New Roman", Times, serif;
  --sans: "Latin Modern Sans", "Computer Modern Sans", system-ui, -apple-system,
          "Segoe UI", Helvetica, Arial, sans-serif;
}

*, *::before, *::after { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--serif);
  font-size: 1.0625rem;
  line-height: 1.65;
}

/* Skip link */
.skip-link {
  position: absolute;
  left: 0.5rem;
  top: -3rem;
  background: #000;
  color: #fff;
  padding: 0.5rem 0.9rem;
  z-index: 100;
  font-family: var(--sans);
  font-size: 0.9rem;
  text-decoration: none;
  transition: top 0.15s ease;
}
.skip-link:focus { top: 0.5rem; color: #fff; }

/* Focus visibility everywhere */
a:focus-visible,
button:focus-visible,
input:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
}

/* ---------- Archive masthead ---------- */
.archive-header {
  border-bottom: 3px double var(--rule);
  padding: 2.5rem 1.25rem 1.75rem;
  text-align: center;
}
.archive-kicker {
  font-family: var(--sans);
  font-size: 0.72rem;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--muted);
  margin: 0 0 0.75rem;
}
.archive-title {
  font-size: clamp(1.6rem, 4.5vw, 2.4rem);
  font-weight: 700;
  letter-spacing: 0.06em;
  margin: 0;
  line-height: 1.2;
  text-transform: uppercase;
}
.archive-subtitle {
  margin: 0.6rem 0 0;
  font-style: italic;
  color: var(--muted);
  font-size: 1rem;
}
.archive-meta {
  margin-top: 1rem;
  font-family: var(--sans);
  font-size: 0.78rem;
  color: var(--muted);
}

/* ---------- Layout ---------- */
.archive-main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.25rem 3rem;
}

.controls {
  padding: 1.5rem 0 0.5rem;
  border-bottom: 1px solid var(--hairline);
}

.controls label {
  font-family: var(--sans);
  font-size: 0.8rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  display: block;
  margin-bottom: 0.4rem;
}

.search-row { display: flex; gap: 0.6rem; }

input[type="search"] {
  flex: 1;
  font-family: var(--serif);
  font-size: 1rem;
  padding: 0.55rem 0.7rem;
  border: 1px solid var(--ink);
  border-radius: 0; /* avoid glassy rounded look */
  background: #fff;
  color: var(--ink);
  min-width: 0;
}

.filters {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin: 0.9rem 0 1.2rem;
  padding: 0;
  list-style: none;
}
.filters button {
  font-family: var(--sans);
  font-size: 0.8rem;
  letter-spacing: 0.04em;
  background: #fff;
  color: var(--ink);
  border: 1px solid var(--ink);
  border-radius: 0;
  padding: 0.35rem 0.8rem;
  cursor: pointer;
}
.filters button[aria-pressed="true"] {
  background: #000;
  color: #fff;
}
.filters button:hover { background: #eee; }
.filters button[aria-pressed="true"]:hover { background: #000; }

/* ---------- Catalogue ---------- */
.catalogue {
  list-style: none;
  margin: 0;
  padding: 0;
}
.paper-entry {
  padding: 1.75rem 0;
  border-bottom: 1px solid var(--hairline);
  display: grid;
  grid-template-columns: 3rem 1fr;
  gap: 0 1rem;
}
.paper-number {
  font-size: 1.4rem;
  color: var(--muted);
  font-variant-numeric: tabular-nums;
  line-height: 1.3;
}
.paper-title {
  font-size: 1.25rem;
  margin: 0 0 0.15rem;
  line-height: 1.35;
  text-transform: uppercase;
  letter-spacing: 0.02em;
}
.paper-classification {
  font-style: italic;
  color: var(--muted);
  margin: 0 0 0.5rem;
  font-size: 0.98rem;
}
.paper-facts {
  font-family: var(--sans);
  font-size: 0.78rem;
  color: var(--ink);
  margin: 0 0 0.6rem;
}
.paper-desc {
  margin: 0 0 1rem;
  max-width: 36rem;
}
.read-row {
  display: flex;
  justify-content: flex-end;
}
.btn-read {
  display: inline-block;
  font-family: var(--sans);
  font-size: 0.82rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  text-decoration: none;
  color: #fff;
  background: #000;
  border: 1px solid #000;
  padding: 0.6rem 1.2rem;
  min-height: 44px;
  line-height: 1.4;
}
.btn-read:hover { background: #333; border-color: #333; }

.archive-count {
  text-align: center;
  font-style: italic;
  color: var(--muted);
  margin: 2rem 0 0;
}
.no-results {
  padding: 2rem 0;
  text-align: center;
  font-style: italic;
}

.archive-footer {
  border-top: 3px double var(--rule);
  text-align: center;
  padding: 1.5rem 1.25rem 2.5rem;
  font-size: 0.9rem;
  color: var(--muted);
}
.archive-footer p { margin: 0.3rem 0; }
.archive-footer a { color: var(--ink); }

/* ---------- Generic paper-sheet styles (optional reuse) ---------- */
/* Individual papers embed their own copy so they stay standalone. */
.sheet {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.25rem 4rem;
}
.topnav {
  font-family: var(--sans);
  font-size: 0.82rem;
  padding: 0.9rem 1.25rem;
  border-bottom: 1px solid var(--hairline);
  max-width: var(--max-width);
  margin: 0 auto;
  display: flex;
  justify-content: space-between;
  gap: 1rem;
}
.topnav a { color: var(--ink); }

/* ---------- Responsive ---------- */
@media (max-width: 560px) {
  body { font-size: 1rem; }
  .paper-entry { grid-template-columns: 1fr; }
  .paper-number { margin-bottom: 0.25rem; font-size: 1rem; }
  .read-row { justify-content: stretch; }
  .btn-read {
    display: block;
    width: 100%;
    text-align: center;
  }
}

/* Equations must not break layout on small screens */
mjx-container[jax="CHTML"][display="true"] {
  overflow-x: auto;
  overflow-y: hidden;
  max-width: 100%;
}

/* Print: clean paper output */
@media print {
  .archive-header, .controls, .filters, .read-row, .archive-footer { display: none; }
  body { font-size: 11pt; }
}