:root {
  --bg: #0f172a;
  --card: #1e293b;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --accent2: #a78bfa;
  --success: #34d399;
  --warn: #fbbf24;
  --danger: #f87171;
}

* { box-sizing: border-box; margin: 0; padding: 0; }

body {
  font-family: 'Segoe UI', system-ui, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
}

.container {
  max-width: 960px;
  margin: 0 auto;
  padding: 0 1rem;
}

/* Navbar */
.navbar {
  background: var(--card);
  border-bottom: 1px solid #334155;
  padding: 1rem 0;
}
.navbar .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.logo {
  font-size: 1.4rem;
  font-weight: 700;
  color: var(--accent);
  text-decoration: none;
}
.nav-links {
  display: flex;
  gap: 1.5rem;
}
.nav-links a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.95rem;
}
.nav-links a:hover, .nav-links a.active {
  color: var(--accent);
}

/* Hero */
.hero {
  text-align: center;
  padding: 3rem 1rem 2rem;
}
.hero h1 {
  font-size: 2rem;
  margin-bottom: 0.5rem;
}
.hero p {
  color: var(--muted);
  max-width: 560px;
  margin: 0 auto;
}

/* Generate Box */
.generate-box {
  background: var(--card);
  border-radius: 12px;
  padding: 1.5rem;
  margin-bottom: 2rem;
  border: 1px solid #334155;
}
.generate-box h2 {
  margin-bottom: 1rem;
  font-size: 1.2rem;
}
.gen-form {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
}
.gen-form input {
  flex: 1;
  min-width: 200px;
  padding: 0.75rem 1rem;
  border-radius: 8px;
  border: 1px solid #475569;
  background: #0f172a;
  color: var(--text);
  font-size: 1rem;
}
.gen-form select {
  padding: 0.75rem 1rem;
  border-radius: 8px;
  border: 1px solid #475569;
  background: #0f172a;
  color: var(--text);
  font-size: 1rem;
  min-width: 180px;
}
.gen-form button {
  padding: 0.75rem 1.5rem;
  border-radius: 8px;
  border: none;
  background: var(--accent);
  color: #0f172a;
  font-weight: 700;
  cursor: pointer;
  font-size: 1rem;
}
.gen-form button:hover { background: #7dd3fc; }
.hint {
  text-align: center;
  color: var(--muted);
  font-size: 0.85rem;
  margin-top: 0.75rem;
}
.hint a { color: var(--accent); }

/* Prompt Form */
.prompt-form {
  display: flex;
  flex-direction: column;
  gap: 1rem;
}
.prompt-form label {
  font-weight: 600;
  font-size: 0.95rem;
  color: var(--text);
}
.prompt-form input,
.prompt-form textarea {
  padding: 0.75rem 1rem;
  border-radius: 8px;
  border: 1px solid #475569;
  background: #0f172a;
  color: var(--text);
  font-size: 0.95rem;
  font-family: inherit;
}
.prompt-form textarea {
  resize: vertical;
  line-height: 1.6;
}
.prompt-form button {
  align-self: flex-start;
  padding: 0.75rem 1.5rem;
  border-radius: 8px;
  border: none;
  background: var(--success);
  color: #064e3b;
  font-weight: 700;
  cursor: pointer;
  font-size: 1rem;
}

/* Topics Grid */
.topics h2 {
  margin-bottom: 1rem;
}
.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 1rem;
}
.topic-card {
  background: var(--card);
  border: 1px solid #334155;
  border-radius: 10px;
  padding: 1.25rem;
  text-decoration: none;
  color: inherit;
  transition: transform .15s, border-color .15s;
}
.topic-card:hover {
  transform: translateY(-2px);
  border-color: var(--accent);
}
.topic-card h3 {
  font-size: 1.1rem;
  margin-bottom: 0.5rem;
}
.meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--muted);
  font-size: 0.85rem;
  margin-bottom: 0.5rem;
}
.prompt-badge {
  background: #4c1d95;
  color: #c4b5fd;
  padding: 2px 8px;
  border-radius: 12px;
  font-size: 0.75rem;
  font-weight: 700;
}
.prompt-badge.default {
  background: #334155;
  color: var(--muted);
}
.diff-badges { display: flex; gap: 4px; }
.badge {
  padding: 2px 8px;
  border-radius: 12px;
  font-size: 0.75rem;
  font-weight: 700;
}
.badge.d1 { background: #064e3b; color: #34d399; }
.badge.d2 { background: #713f12; color: #fbbf24; }
.badge.d3 { background: #7c2d12; color: #fb923c; }
.badge.d4 { background: #7f1d1d; color: #f87171; }

.empty {
  text-align: center;
  color: var(--muted);
  padding: 3rem;
}

/* Prompt Grid */
.prompt-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 1rem;
}
.prompt-card {
  background: var(--card);
  border: 1px solid #334155;
  border-radius: 10px;
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
}
.prompt-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 0.75rem;
}
.prompt-header h3 {
  font-size: 1.1rem;
}
.prompt-id {
  color: var(--muted);
  font-size: 0.75rem;
}
.prompt-body {
  flex: 1;
  margin-bottom: 1rem;
}
.prompt-section {
  margin-bottom: 0.75rem;
}
.prompt-section strong {
  display: block;
  font-size: 0.85rem;
  color: var(--muted);
  margin-bottom: 0.3rem;
}
.prompt-section pre {
  background: #0f172a;
  padding: 0.6rem;
  border-radius: 6px;
  font-size: 0.85rem;
  color: var(--text);
  white-space: pre-wrap;
  border: 1px solid #334155;
}
.prompt-footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-top: 1px solid #334155;
  padding-top: 0.75rem;
}
.prompt-footer .date {
  color: var(--muted);
  font-size: 0.85rem;
}
.btn-danger {
  background: var(--danger);
  color: #7f1d1d;
  border: none;
  padding: 0.4rem 0.8rem;
  border-radius: 6px;
  font-weight: 700;
  cursor: pointer;
  font-size: 0.85rem;
}

/* History Table */
.history-table {
  width: 100%;
  border-collapse: collapse;
  background: var(--card);
  border-radius: 10px;
  overflow: hidden;
  border: 1px solid #334155;
}
.history-table th,
.history-table td {
  padding: 0.9rem 1rem;
  text-align: left;
  border-bottom: 1px solid #334155;
}
.history-table th {
  background: #0f172a;
  color: var(--muted);
  font-size: 0.85rem;
  font-weight: 600;
}
.history-table td {
  font-size: 0.9rem;
}
.history-table tr:hover td {
  background: #0f172a;
}
.history-table .date {
  color: var(--muted);
  font-size: 0.85rem;
  white-space: nowrap;
}
.status {
  padding: 3px 10px;
  border-radius: 12px;
  font-size: 0.8rem;
  font-weight: 700;
}
.status.success { background: #064e3b; color: #34d399; }
.status.error { background: #7f1d1d; color: #f87171; }
.btn-sm {
  display: inline-block;
  padding: 0.3rem 0.7rem;
  background: var(--accent);
  color: #0f172a;
  text-decoration: none;
  border-radius: 6px;
  font-size: 0.85rem;
  font-weight: 700;
}

/* Topic Page */
.topic-header {
  padding: 2rem 0 1rem;
}
.topic-header h1 {
  font-size: 1.8rem;
}
.stats {
  display: flex;
  gap: 1rem;
  margin-top: 0.5rem;
}
.stat {
  background: var(--card);
  padding: 0.4rem 0.9rem;
  border-radius: 20px;
  font-size: 0.85rem;
  color: var(--muted);
  border: 1px solid #334155;
}

/* Tabs */
.tabs {
  display: flex;
  gap: 0.5rem;
  margin: 1.5rem 0 1rem;
  border-bottom: 1px solid #334155;
}
.tab-btn {
  background: transparent;
  border: none;
  color: var(--muted);
  padding: 0.6rem 1rem;
  cursor: pointer;
  font-size: 0.95rem;
  border-bottom: 2px solid transparent;
}
.tab-btn.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
}
.tab-panel { display: none; }
.tab-panel.active { display: block; }

/* Markdown box */
.markdown-box pre {
  background: var(--card);
  padding: 1.5rem;
  border-radius: 10px;
  overflow-x: auto;
  white-space: pre-wrap;
  font-family: inherit;
  line-height: 1.7;
  border: 1px solid #334155;
}

/* Questions */
.filter-bar {
  display: flex;
  gap: 0.5rem;
  margin-bottom: 1rem;
  flex-wrap: wrap;
}
.filter-btn {
  background: var(--card);
  border: 1px solid #334155;
  color: var(--muted);
  padding: 0.4rem 0.9rem;
  border-radius: 20px;
  cursor: pointer;
  font-size: 0.85rem;
}
.filter-btn.active {
  background: var(--accent);
  color: #0f172a;
  border-color: var(--accent);
}

.q-card {
  background: var(--card);
  border: 1px solid #334155;
  border-radius: 10px;
  padding: 1.25rem;
  margin-bottom: 1rem;
}
.q-header {
  display: flex;
  justify-content: space-between;
  margin-bottom: 0.75rem;
}
.q-id {
  color: var(--muted);
  font-size: 0.85rem;
}
.q-diff {
  padding: 2px 10px;
  border-radius: 12px;
  font-size: 0.75rem;
  font-weight: 700;
}
.q-diff.d1 { background: #064e3b; color: #34d399; }
.q-diff.d2 { background: #713f12; color: #fbbf24; }
.q-diff.d3 { background: #7c2d12; color: #fb923c; }
.q-diff.d4 { background: #7f1d1d; color: #f87171; }
.q-text {
  font-size: 1.05rem;
  margin-bottom: 0.75rem;
}
.options {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.6rem;
  margin-bottom: 0.75rem;
}
.option {
  background: #0f172a;
  border: 1px solid #475569;
  padding: 0.6rem 0.9rem;
  border-radius: 8px;
  font-size: 0.95rem;
}
.option.correct {
  border-color: var(--success);
  background: #064e3b;
  color: #34d399;
}
.explanation {
  background: #0f172a;
  padding: 0.75rem 1rem;
  border-radius: 8px;
  font-size: 0.9rem;
  color: var(--muted);
  border-left: 3px solid var(--accent);
}

/* JSON box */
.json-box {
  background: var(--card);
  padding: 1.5rem;
  border-radius: 10px;
  overflow-x: auto;
  font-size: 0.85rem;
  border: 1px solid #334155;
}

/* Footer */
footer {
  text-align: center;
  padding: 2rem 0;
  color: var(--muted);
  font-size: 0.85rem;
  margin-top: 2rem;
  border-top: 1px solid #334155;
}
footer a {
  color: var(--accent);
  text-decoration: none;
}

.btn {
  display: inline-block;
  padding: 0.6rem 1.2rem;
  background: var(--accent);
  color: #0f172a;
  text-decoration: none;
  border-radius: 8px;
  font-weight: 700;
}