/* ── Reset & Base ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg: #f9f9f7;
  --surface: #ffffff;
  --border: #e5e5e0;
  --text: #1a1a1a;
  --muted: #6b6b6b;
  --accent: #2563eb;
  --accent-light: #eff6ff;
  --tag-bg: #f1f5f9;
  --tag-text: #334155;
  --high: #16a34a;
  --high-bg: #f0fdf4;
  --mid: #ca8a04;
  --mid-bg: #fefce8;
  --low: #6b7280;
  --low-bg: #f9fafb;
  --radius: 10px;
  --shadow: 0 1px 3px rgba(0,0,0,0.07), 0 1px 2px rgba(0,0,0,0.04);
}

body {
  font-family: 'Inter', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

/* ── Header ── */
header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  position: sticky;
  top: 0;
  z-index: 10;
}

.header-inner {
  max-width: 900px;
  margin: 0 auto;
  padding: 1.25rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.logo {
  font-size: 2rem;
  line-height: 1;
}

header h1 {
  font-family: 'Lora', serif;
  font-size: 1.35rem;
  font-weight: 600;
  color: var(--text);
  line-height: 1.2;
}

.subtitle {
  font-size: 0.8rem;
  color: var(--muted);
  margin-top: 0.1rem;
}

.meta {
  font-size: 0.78rem;
  color: var(--muted);
  text-align: right;
  white-space: nowrap;
}

/* ── Filters ── */
.filters {
  max-width: 900px;
  margin: 0 auto;
  padding: 0.6rem 1.5rem 0.75rem;
  display: flex;
  gap: 0.4rem;
  flex-wrap: wrap;
}

.filter-btn {
  font-size: 0.75rem;
  font-family: inherit;
  padding: 0.25rem 0.75rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--muted);
  cursor: pointer;
  transition: all 0.15s;
}

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

.filter-btn.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}

/* ── Main ── */
main {
  flex: 1;
  max-width: 900px;
  margin: 0 auto;
  padding: 1.5rem;
  width: 100%;
}

/* ── Paper Cards ── */
.papers-grid {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.paper-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
  box-shadow: var(--shadow);
  transition: box-shadow 0.15s;
}

.paper-card:hover {
  box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

.card-top {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 0.5rem;
}

.paper-title {
  font-family: 'Lora', serif;
  font-size: 1.05rem;
  font-weight: 600;
  line-height: 1.4;
  color: var(--text);
}

.paper-title a {
  color: inherit;
  text-decoration: none;
}

.paper-title a:hover {
  color: var(--accent);
}

.relevance-badge {
  flex-shrink: 0;
  font-size: 0.7rem;
  font-weight: 600;
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
  letter-spacing: 0.03em;
  text-transform: uppercase;
}

.relevance-high { background: var(--high-bg); color: var(--high); }
.relevance-medium { background: var(--mid-bg); color: var(--mid); }
.relevance-low { background: var(--low-bg); color: var(--low); }

.paper-meta {
  font-size: 0.8rem;
  color: var(--muted);
  margin-bottom: 0.6rem;
}

.paper-meta .journal {
  font-style: italic;
}

.paper-abstract {
  font-size: 0.875rem;
  color: #444;
  line-height: 1.65;
  margin-bottom: 0.75rem;
}

.card-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.tags {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.tag {
  font-size: 0.7rem;
  background: var(--tag-bg);
  color: var(--tag-text);
  border-radius: 4px;
  padding: 0.15rem 0.5rem;
}

.pmid-link {
  font-size: 0.72rem;
  color: var(--muted);
  text-decoration: none;
}

.pmid-link:hover {
  color: var(--accent);
  text-decoration: underline;
}

/* ── Checkbox ── */
.checkbox-wrap {
  display: flex;
  align-items: center;
  flex-shrink: 0;
  cursor: pointer;
  margin-right: 0.25rem;
}

.checkbox-wrap input[type="checkbox"] {
  display: none;
}

.checkmark {
  width: 18px;
  height: 18px;
  border: 2px solid var(--border);
  border-radius: 4px;
  background: var(--surface);
  transition: all 0.15s;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.checkbox-wrap:hover .checkmark {
  border-color: var(--accent);
}

.paper-checkbox:checked + .checkmark {
  background: var(--accent);
  border-color: var(--accent);
}

.paper-checkbox:checked + .checkmark::after {
  content: '';
  display: block;
  width: 5px;
  height: 9px;
  border: 2px solid #fff;
  border-top: none;
  border-left: none;
  transform: rotate(45deg) translate(-1px, -1px);
}

.paper-card.selected {
  border-color: var(--accent);
  box-shadow: 0 0 0 2px var(--accent-light), var(--shadow);
}

/* ── Download Bar ── */
.download-bar {
  position: fixed;
  bottom: 1.5rem;
  left: 50%;
  transform: translateX(-50%);
  background: var(--text);
  color: #fff;
  border-radius: 999px;
  padding: 0.65rem 0.75rem 0.65rem 1.25rem;
  display: flex;
  align-items: center;
  gap: 0.75rem;
  box-shadow: 0 4px 20px rgba(0,0,0,0.25);
  font-size: 0.85rem;
  z-index: 100;
  white-space: nowrap;
  transition: opacity 0.2s, transform 0.2s;
}

.download-bar.hidden {
  opacity: 0;
  pointer-events: none;
  transform: translateX(-50%) translateY(8px);
}

.bar-actions {
  display: flex;
  gap: 0.4rem;
}

.bar-btn {
  font-family: inherit;
  font-size: 0.8rem;
  font-weight: 500;
  padding: 0.35rem 0.85rem;
  border-radius: 999px;
  border: none;
  cursor: pointer;
  transition: opacity 0.15s;
}

.bar-btn:hover { opacity: 0.85; }

.bar-btn.secondary {
  background: rgba(255,255,255,0.15);
  color: #fff;
}

.bar-btn.primary {
  background: #fff;
  color: var(--text);
}

/* ── Empty state ── */
.empty {
  text-align: center;
  padding: 4rem 2rem;
  color: var(--muted);
}

.hidden { display: none; }

/* ── Footer ── */
footer {
  text-align: center;
  padding: 1.5rem;
  font-size: 0.78rem;
  color: var(--muted);
  border-top: 1px solid var(--border);
  background: var(--surface);
}

/* ── Responsive ── */
@media (max-width: 600px) {
  .header-inner { flex-direction: column; align-items: flex-start; }
  .meta { text-align: left; }
  .card-top { flex-direction: column; }
}