:root {
  --bg: #f7f7fb;
  --card-bg: #ffffff;
  --border: #e3e3ea;
  --text: #1f2430;
  --text-muted: #656b7a;
  --accent: #3457d5;
  --accent-light: #eef1fd;
  --error-bg: #fdecec;
  --error-text: #a6303a;
  --radius: 10px;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
}

header {
  max-width: 760px;
  margin: 0 auto;
  padding: 2.5rem 1.25rem 1rem;
  text-align: center;
}

header h1 { margin: 0 0 0.4rem; font-size: 1.9rem; }
.tagline { color: var(--text-muted); margin: 0 auto; max-width: 560px; font-size: 0.95rem; }

main {
  max-width: 760px;
  margin: 0 auto;
  padding: 0 1.25rem 3rem;
  display: flex;
  flex-direction: column;
  gap: 1.25rem;
}

.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.25rem 1.5rem;
}

.hidden { display: none !important; }

/* --- Banner --- */
.banner {
  max-width: 760px;
  margin: 0 auto;
  padding: 0.6rem 1.25rem;
  text-align: center;
  font-size: 0.9rem;
  background: var(--accent-light);
  color: var(--accent);
}

/* --- Input --- */
#paper-form {
  display: flex;
  gap: 0.5rem;
}

#paper-input {
  flex: 1;
  padding: 0.6rem 0.8rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 0.95rem;
}

button {
  cursor: pointer;
  border: none;
  border-radius: 8px;
  padding: 0.6rem 1.1rem;
  font-size: 0.95rem;
  background: var(--accent);
  color: white;
  transition: opacity 0.15s;
}

button:hover { opacity: 0.9; }
button:disabled { opacity: 0.5; cursor: not-allowed; }

label { font-size: 0.85rem; font-weight: 600; color: var(--text-muted); display: block; margin-bottom: 0.4rem; }

.chips {
  margin-top: 0.75rem;
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  align-items: center;
}

.chip-label { font-size: 0.85rem; color: var(--text-muted); }

.chip {
  background: var(--accent-light);
  color: var(--accent);
  border-radius: 999px;
  padding: 0.3rem 0.75rem;
  font-size: 0.82rem;
}

/* --- Paper card --- */
#paper-title { margin: 0 0 0.3rem; font-size: 1.3rem; }
.meta { color: var(--text-muted); font-size: 0.9rem; margin: 0 0 0.3rem; }
.stats { font-size: 0.9rem; margin: 0 0 0.75rem; }
.stats strong { color: var(--accent); }
.abstract { font-size: 0.95rem; }

/* --- Explain --- */
.slider-row { margin-bottom: 1rem; }
#level-slider { width: 100%; }
.slider-labels {
  display: flex;
  justify-content: space-between;
  font-size: 0.8rem;
  color: var(--text-muted);
  margin-top: 0.25rem;
}
#explain-text { font-size: 0.97rem; }

/* --- What next --- */
.ai-summary {
  background: var(--accent-light);
  border-radius: 8px;
  padding: 0.75rem 1rem;
  font-size: 0.92rem;
}
#whatnext-list { list-style: none; padding: 0; margin: 0.75rem 0 0; }
#whatnext-list li {
  padding: 0.55rem 0;
  border-top: 1px solid var(--border);
  font-size: 0.9rem;
}
#whatnext-list li:first-child { border-top: none; }
#whatnext-list a { color: var(--accent); }
.citing-year { color: var(--text-muted); font-size: 0.82rem; }

/* --- Trend --- */
.trend-query-row { display: flex; gap: 0.5rem; margin-bottom: 1rem; }
#trend-query {
  flex: 1;
  padding: 0.5rem 0.7rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 0.88rem;
}

/* --- States --- */
.loading { color: var(--text-muted); font-size: 0.9rem; font-style: italic; }
.error {
  background: var(--error-bg);
  color: var(--error-text);
  border-radius: 8px;
  padding: 0.6rem 0.9rem;
  font-size: 0.9rem;
  margin-top: 0.5rem;
}

footer {
  text-align: center;
  color: var(--text-muted);
  font-size: 0.8rem;
  padding-bottom: 2rem;
}
footer a { color: var(--accent); }

@media (max-width: 480px) {
  #paper-form { flex-direction: column; }
}