/* ═══════════════════════════════════════════════════════════════════
 *  Research Papers — archive + single-paper page styles.
 *  Wraps in .ptst-content-page so .container sizing cascades in
 *  from ptst-content-pages.css.
 * ═══════════════════════════════════════════════════════════════════ */

/* ── Archive hero — uses the shared .page-hero pattern from
 *    ptst-content-pages.css (photo bg + scrim + white headings).
 *    No per-page hero rules needed here.
 *
 *    The single-paper page keeps its lighter tint band — research
 *    detail pages don't need a photo hero; legibility wins.
 * --------------------------------------------------------------- */
.ptst-research-paper__hero {
    padding: 24px 0 28px;
    background: var(--bg-soft, #F4F7FB);
    border-bottom: 1px solid var(--line, #E2E8F2);
}

/* ── Breadcrumb — sits below the hero on the body bg, mirrors the
 *    convention used by the Course archive (.course-archive__crumb).
 *    Small top + bottom padding so the breadcrumb isn't flush.
 * --------------------------------------------------------------- */
.ptst-research-papers > .container,
.ptst-research-paper-single > .container {
    padding-top: 18px;
    padding-bottom: 4px;
}
.ptst-research-papers .ptst-crumb,
.ptst-research-paper-single .ptst-crumb {
    display: flex; align-items: center; gap: 8px;
    font-size: 13px; color: var(--ink-3, #5A6B86);
    padding: 0;
}
.ptst-research-papers .ptst-crumb a,
.ptst-research-paper-single .ptst-crumb a { color: var(--ink-3, #5A6B86); text-decoration: none; }
.ptst-research-papers .ptst-crumb a:hover,
.ptst-research-paper-single .ptst-crumb a:hover { color: var(--brand-blue, #0E4A9C); text-decoration: underline; text-underline-offset: 3px; }
.ptst-research-papers .ptst-crumb__sep,
.ptst-research-paper-single .ptst-crumb__sep { color: var(--ink-4, #93A1B8); }
.ptst-research-papers .ptst-crumb__current,
.ptst-research-paper-single .ptst-crumb__current { color: var(--ink, #0B1B33); }

/* ── Topic filter pills ────────────────────────────────────────── */
.ptst-research-papers__filter-section { padding: 20px 0 0; }
.ptst-topic-filter {
    display: flex; flex-wrap: wrap; gap: 8px;
}
.ptst-topic-pill {
    display: inline-flex; align-items: center; gap: 6px;
    padding: 7px 14px;
    background: #fff;
    border: 1px solid var(--line, #E2E8F2);
    border-radius: 999px;
    font-size: 13.5px;
    font-weight: 600;
    color: var(--ink-2, #2A3D5C);
    text-decoration: none;
    transition: background 120ms ease, border-color 120ms ease, color 120ms ease;
}
.ptst-topic-pill:hover {
    border-color: var(--brand-blue, #0E4A9C);
    color: var(--brand-blue, #0E4A9C);
}
.ptst-topic-pill.is-active {
    background: var(--brand-blue, #0E4A9C);
    border-color: var(--brand-blue, #0E4A9C);
    color: #fff;
}
.ptst-topic-pill.is-active:hover { color: #fff; }
.ptst-topic-pill__count {
    display: inline-block;
    padding: 1px 7px;
    border-radius: 999px;
    background: rgba(11, 27, 51, 0.06);
    font-size: 11.5px;
    font-weight: 700;
    color: var(--ink-3, #5A6B86);
    line-height: 1.4;
}
.ptst-topic-pill.is-active .ptst-topic-pill__count {
    background: rgba(255,255,255,0.22);
    color: #fff;
}
.ptst-topic-pill--sm {
    padding: 4px 10px;
    font-size: 12px;
}

/* ── Paper grid + cards ────────────────────────────────────────── */
.ptst-research-papers__grid-section { padding: 28px 0 80px; }
.ptst-paper-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
    gap: 24px;
}
.ptst-paper-card {
    display: flex; flex-direction: column;
    background: #fff;
    border: 1px solid var(--line, #E2E8F2);
    border-radius: 14px;
    overflow: hidden;
    text-decoration: none;
    color: var(--ink, #0B1B33);
    transition: transform 120ms ease, border-color 120ms ease, box-shadow 120ms ease;
}
.ptst-paper-card:hover {
    transform: translateY(-2px);
    border-color: var(--brand-blue, #0E4A9C);
    box-shadow: 0 12px 32px -16px rgba(11, 27, 51, 0.22);
}
/* The card is an <a>; suppress the global a:hover underline rule on every
   descendant so only the card's shadow / lift signals the hover. The card
   title gets a subtle blue colour shift instead. */
.ptst-paper-card,
.ptst-paper-card:hover,
.ptst-paper-card:focus,
.ptst-paper-card:hover *,
.ptst-paper-card:focus * { text-decoration: none; }
.ptst-paper-card:hover .ptst-paper-card__title,
.ptst-paper-card:focus .ptst-paper-card__title { color: var(--brand-blue, #0E4A9C); }
.ptst-paper-card__cover {
    aspect-ratio: 5 / 4;
    background-size: cover;
    background-position: center;
    background-color: var(--bg-soft, #F4F7FB);
    display: flex; align-items: center; justify-content: center;
    border-bottom: 1px solid var(--line, #E2E8F2);
}
.ptst-paper-card__cover svg {
    width: 56px; height: 56px;
    fill: var(--ink-4, #93A1B8);
    opacity: 0.6;
}
.ptst-paper-card__cover--photo svg { display: none; }
.ptst-paper-card__body {
    padding: 16px 18px 20px;
    display: flex; flex-direction: column; gap: 6px;
}
.ptst-paper-card__year {
    font-size: 11px;
    font-weight: 800;
    letter-spacing: 0.12em;
    text-transform: uppercase;
    color: var(--brand-blue, #0E4A9C);
}
.ptst-paper-card__title {
    margin: 0;
    font-size: 17px;
    font-weight: 700;
    line-height: 1.3;
    letter-spacing: -0.01em;
    color: var(--ink, #0B1B33);
}
.ptst-paper-card__authors {
    margin: 4px 0 0;
    font-size: 13px;
    color: var(--ink-3, #5A6B86);
}
.ptst-paper-card__excerpt {
    margin: 6px 0 0;
    font-size: 13.5px;
    line-height: 1.5;
    color: var(--ink-2, #2A3D5C);
}

/* ── Empty state ───────────────────────────────────────────────── */
.ptst-empty-state {
    padding: 60px 0;
    text-align: center;
    font-size: 16px;
    color: var(--ink-3, #5A6B86);
}

/* ── Pagination ────────────────────────────────────────────────── */
.ptst-pagination {
    display: flex; justify-content: center; align-items: center;
    gap: 6px;
    margin-top: 40px;
    flex-wrap: wrap;
}
.ptst-pagination .page-numbers {
    display: inline-flex; align-items: center; justify-content: center;
    min-width: 36px; height: 36px;
    padding: 0 12px;
    background: #fff;
    border: 1px solid var(--line, #E2E8F2);
    border-radius: 8px;
    font-size: 14px;
    font-weight: 600;
    color: var(--ink-2, #2A3D5C);
    text-decoration: none;
    transition: border-color 120ms ease, color 120ms ease;
}
.ptst-pagination .page-numbers:hover {
    border-color: var(--brand-blue, #0E4A9C);
    color: var(--brand-blue, #0E4A9C);
}
.ptst-pagination .page-numbers.current {
    background: var(--brand-blue, #0E4A9C);
    border-color: var(--brand-blue, #0E4A9C);
    color: #fff;
}
.ptst-pagination .page-numbers.dots { border: 0; background: transparent; }


/* ═══════════════════════════════════════════════════════════════════
 *  Single paper page
 * ═══════════════════════════════════════════════════════════════════ */
.ptst-research-paper {
    max-width: 72ch;
    margin: 0;     /* left-aligned, flows from the breadcrumb */
}
.ptst-research-paper__topics {
    display: flex; flex-wrap: wrap; gap: 6px;
    margin: 18px 0 16px;
}
.ptst-research-paper__title {
    margin: 0 0 12px;
    font-size: 38px;
    font-weight: 800;
    line-height: 1.1;
    letter-spacing: -0.018em;
    color: var(--ink, #0B1B33);
    text-wrap: balance;
}
.ptst-research-paper__meta {
    display: flex; align-items: center; flex-wrap: wrap;
    gap: 6px 10px;
    font-size: 14.5px;
    color: var(--ink-3, #5A6B86);
}
.ptst-research-paper__authors { font-weight: 600; color: var(--ink-2, #2A3D5C); }
.ptst-research-paper__sep { color: var(--ink-4, #93A1B8); }
.ptst-research-paper__cover {
    margin: 28px 0 0;
    border-radius: 12px;
    overflow: hidden;
    border: 1px solid var(--line, #E2E8F2);
}
.ptst-research-paper__cover img {
    display: block; width: 100%; height: auto;
}
.ptst-research-paper__abstract {
    margin: 32px 0 0;
}
.ptst-research-paper__abstract h2 {
    font-size: 22px;
    font-weight: 800;
    color: var(--ink, #0B1B33);
    margin: 0 0 10px;
    letter-spacing: -0.014em;
}
.ptst-research-paper__abstract p {
    font-size: 16px;
    line-height: 1.7;
    color: var(--ink-2, #2A3D5C);
    margin: 0 0 1.1em;
}
.ptst-research-paper__actions {
    margin: 32px 0 0;
    display: flex; flex-wrap: wrap; gap: 12px;
}
.ptst-research-paper__actions .btn__hint {
    font-size: 12px;
    opacity: 0.85;
    font-weight: 400;
    margin-left: 4px;
}
@media (max-width: 640px) {
    .ptst-research-paper__title { font-size: 28px; }
}