:root {
  --bg: #f5f6fa;
  --sidebar-bg: #1a1a2e;
  --sidebar-fg: #d8d8e6;
  --sidebar-active: #6c5ce7;
  --card-bg: #ffffff;
  --text: #22223b;
  --text-muted: #5c5c73;
  --border: #e0e0ea;
  --accent: #6c5ce7;
  --accent-dark: #4834d4;
  --success: #00b894;
  --danger: #d63031;
  --code-bg: #282c34;
  --code-fg: #e6e6e6;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
}

a { color: var(--accent-dark); }

.layout {
  display: flex;
  min-height: 100vh;
}

/* ------------------------------ lock screen ------------------------------ */

#lock-screen[hidden] { display: none; }
#lock-screen {
  min-height: 100vh;
  align-items: center;
  justify-content: center;
  background: var(--sidebar-bg);
  padding: 20px;
}

.lock-card {
  background: var(--card-bg);
  border-radius: 16px;
  padding: 36px 32px;
  max-width: 340px;
  width: 100%;
  text-align: center;
  box-shadow: 0 20px 60px rgba(0,0,0,0.3);
}
.lock-icon { font-size: 2.5rem; margin-bottom: 8px; }
.lock-card h1 { font-size: 1.3rem; margin: 0 0 8px; }
.lock-card p { color: var(--text-muted); font-size: 0.9rem; margin: 0 0 20px; }
.lock-card input {
  width: 100%;
  padding: 10px 14px;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 0.95rem;
  margin-bottom: 12px;
}
.lock-card .btn { width: 100%; }
.lock-error { color: var(--danger); font-size: 0.85rem; margin-top: 12px; }

.sidebar-lock-btn {
  display: block;
  width: calc(100% - 20px);
  margin: 20px 10px 0;
  background: transparent;
  border: 1px solid rgba(255,255,255,0.15);
  color: #9a9ab8;
  border-radius: 8px;
  padding: 8px 12px;
  font-size: 0.8rem;
  cursor: pointer;
}
.sidebar-lock-btn:hover { background: rgba(255,255,255,0.06); color: white; }

/* ------------------------------- sidebar -------------------------------- */

.sidebar {
  width: 280px;
  flex-shrink: 0;
  background: var(--sidebar-bg);
  color: var(--sidebar-fg);
  padding: 20px 0 60px;
  overflow-y: auto;
  height: 100vh;
  position: sticky;
  top: 0;
}

.sidebar-title {
  padding: 0 20px 16px;
  border-bottom: 1px solid rgba(255,255,255,0.1);
  margin-bottom: 10px;
}

.sidebar-title a {
  color: white;
  font-size: 1.2rem;
  font-weight: 700;
  text-decoration: none;
}

#sidebar-nav { padding: 0 10px; }

.nav-home {
  display: block;
  padding: 10px 12px;
  border-radius: 8px;
  color: var(--sidebar-fg);
  text-decoration: none;
  font-weight: 600;
  margin-bottom: 12px;
}
.nav-home:hover, .nav-home.active { background: rgba(255,255,255,0.08); color: white; }

.nav-group { margin-bottom: 6px; }

.nav-group-title {
  display: flex;
  justify-content: space-between;
  padding: 10px 12px 4px;
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: #9a9ab8;
}

.nav-count { font-variant-numeric: tabular-nums; }

.nav-lessons { display: flex; flex-direction: column; }

.nav-tier {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 10px 12px 3px;
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  font-weight: 700;
  color: #8888a8;
}
.nav-tier:first-child { padding-top: 2px; }
.tier-dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  display: inline-block;
  flex-shrink: 0;
}

.badge {
  display: inline-block;
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  padding: 2px 9px;
  border-radius: 999px;
  border: 1px solid;
  vertical-align: middle;
}

.nav-lesson {
  display: flex;
  gap: 8px;
  align-items: flex-start;
  padding: 7px 12px;
  border-radius: 8px;
  color: var(--sidebar-fg);
  text-decoration: none;
  font-size: 0.9rem;
  line-height: 1.3;
}
.nav-lesson:hover { background: rgba(255,255,255,0.06); color: white; }
.nav-lesson.active { background: var(--sidebar-active); color: white; }
.nav-lesson .tick { flex-shrink: 0; }

/* ------------------------------- content -------------------------------- */

.content {
  flex: 1;
  padding: 40px 48px 80px;
  max-width: 900px;
}

.home h1 { margin-top: 0; font-size: 2rem; }
.lede { color: var(--text-muted); font-size: 1.05rem; max-width: 700px; }

.overall-progress { margin: 24px 0 32px; }
.overall-progress-text { font-weight: 600; margin-bottom: 8px; }

.progress-bar {
  background: var(--border);
  border-radius: 999px;
  height: 8px;
  overflow: hidden;
}
.progress-bar.large { height: 12px; }
.progress-fill {
  background: linear-gradient(90deg, var(--accent), var(--success));
  height: 100%;
  border-radius: 999px;
  transition: width 0.3s ease;
}

.tier-legend {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 10px;
  margin: 0 0 32px;
}
.tier-legend-item {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 10px 14px;
  font-size: 0.85rem;
  color: var(--text-muted);
  display: flex;
  gap: 8px;
  align-items: baseline;
}
.tier-legend-item .tier-dot { align-self: center; }
.tier-legend-item strong { color: var(--text); }

.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 16px;
  margin: 24px 0 40px;
}

.topic-card {
  display: block;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px;
  text-decoration: none;
  color: var(--text);
  transition: transform 0.15s ease, box-shadow 0.15s ease;
}
.topic-card:hover { transform: translateY(-2px); box-shadow: 0 8px 20px rgba(0,0,0,0.08); }
.topic-card-icon { font-size: 1.8rem; }
.topic-card h3 { margin: 8px 0 4px; }
.topic-card p { color: var(--text-muted); font-size: 0.9rem; margin: 0 0 14px; min-height: 40px; }
.topic-card-meta { margin-top: 8px; font-size: 0.82rem; color: var(--text-muted); }

.home-footer-note {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px 24px;
  color: var(--text-muted);
}
.home-footer-note h3 { color: var(--text); margin-top: 0; }

/* -------------------------------- lesson --------------------------------- */

.lesson-header .crumb { color: var(--text-muted); font-size: 0.85rem; margin-bottom: 6px; }
.lesson-header h1 { margin-top: 0; }

.block { margin: 20px 0; }
.block-text p:first-child { margin-top: 0; }
.block-text ul, .block-text ol { line-height: 1.7; }

.note {
  border-radius: 10px;
  padding: 14px 16px;
  border: 1px solid var(--border);
  border-left-width: 4px;
}
.note-tip { border-left-color: var(--accent); background: #f4f2ff; }
.note-warning { border-left-color: #e67e22; background: #fff6ec; }
.note-info { border-left-color: #0984e3; background: #eef7ff; }
.note-label { font-weight: 700; margin-bottom: 4px; font-size: 0.85rem; }

.code-caption { font-size: 0.8rem; color: var(--text-muted); margin-bottom: 4px; font-weight: 600; }
.code-block {
  background: var(--code-bg);
  color: var(--code-fg);
  padding: 14px 16px;
  border-radius: 10px;
  overflow-x: auto;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: 0.87rem;
  line-height: 1.5;
}

/* ------------------------------ playgrounds ------------------------------ */

.playground {
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 16px;
  background: var(--card-bg);
}

.playground-task {
  background: #f4f2ff;
  border-radius: 8px;
  padding: 10px 14px;
  margin-bottom: 12px;
  font-size: 0.92rem;
}

.tabs { display: flex; gap: 4px; margin-bottom: 6px; }
.tab-btn {
  border: none;
  background: var(--border);
  color: var(--text-muted);
  padding: 6px 14px;
  border-radius: 6px 6px 0 0;
  cursor: pointer;
  font-size: 0.8rem;
  font-weight: 700;
}
.tab-btn.active { background: var(--code-bg); color: white; }

.tab-panels { position: relative; }
.tab-panel { display: none; }
.tab-panel.active { display: block; }

.code-input {
  width: 100%;
  min-height: 120px;
  background: var(--code-bg);
  color: var(--code-fg);
  border: none;
  border-radius: 0 8px 8px 8px;
  padding: 12px 14px;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: 0.87rem;
  resize: vertical;
  line-height: 1.5;
}

.sql-input, .json-input { border-radius: 8px; min-height: 90px; }

.playground-actions {
  display: flex;
  align-items: center;
  gap: 10px;
  margin: 12px 0;
  flex-wrap: wrap;
}

.playground-preview {
  width: 100%;
  min-height: 160px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: white;
}

.sql-status { font-size: 0.8rem; color: var(--text-muted); }
.sql-status.ready::before { content: "● "; color: var(--success); }

.sql-result, .sql-verify-result, .json-result { margin-top: 10px; }
.sql-loading, .sql-empty { color: var(--text-muted); font-size: 0.9rem; }
.sql-error { color: var(--danger); background: #fdecea; padding: 10px 14px; border-radius: 8px; font-family: monospace; font-size: 0.85rem; }

.sql-table {
  border-collapse: collapse;
  width: 100%;
  font-size: 0.87rem;
}
.sql-table th, .sql-table td {
  border: 1px solid var(--border);
  padding: 6px 10px;
  text-align: left;
}
.sql-table th { background: #f0f0f7; }
.sql-table em { color: var(--text-muted); }

.verify-outcome {
  padding: 10px 14px;
  border-radius: 8px;
  font-size: 0.9rem;
}
.verify-outcome.pass { background: #e8fbf4; color: #027a5b; }
.verify-outcome.fail { background: #fdecea; color: var(--danger); }
.verify-outcome .explain { margin-top: 6px; color: inherit; opacity: 0.85; font-size: 0.85rem; }

/* -------------------------------- predict --------------------------------- */

.predict-options { display: flex; flex-direction: column; gap: 8px; margin: 12px 0; }
.predict-option {
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 8px 12px;
  display: flex;
  gap: 10px;
  align-items: center;
  cursor: pointer;
}
.predict-option:hover { background: #f9f9fc; }
.predict-result { margin-top: 12px; }

/* ---------------------------------- quiz ---------------------------------- */

.quiz {
  margin-top: 40px;
  border-top: 2px solid var(--border);
  padding-top: 24px;
}
.quiz h2 { margin-top: 0; }

.quiz-question { margin-bottom: 20px; }
.quiz-q-text { font-weight: 600; margin-bottom: 8px; }
.quiz-choices { display: flex; flex-direction: column; gap: 6px; }

.quiz-choice {
  display: flex;
  gap: 10px;
  align-items: center;
  padding: 8px 12px;
  border: 1px solid var(--border);
  border-radius: 8px;
  cursor: pointer;
}
.quiz-choice:hover { background: #f9f9fc; }
.quiz-choice.correct { border-color: var(--success); background: #e8fbf4; }
.quiz-choice.incorrect { border-color: var(--danger); background: #fdecea; }

.quiz-explain {
  margin-top: 8px;
  font-size: 0.87rem;
  color: var(--text-muted);
  background: #f7f7fb;
  padding: 8px 12px;
  border-radius: 8px;
}

.quiz-score { margin-top: 14px; font-weight: 700; font-size: 1.05rem; }

/* --------------------------------- buttons --------------------------------- */

.btn {
  display: inline-block;
  border: none;
  border-radius: 8px;
  padding: 9px 18px;
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  text-decoration: none;
  text-align: center;
}
.btn-primary { background: var(--accent); color: white; }
.btn-primary:hover { background: var(--accent-dark); }
.btn-secondary { background: var(--border); color: var(--text); }
.btn-secondary:hover { background: #d3d3e0; }

.lesson-footer {
  margin-top: 40px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 16px;
  flex-wrap: wrap;
}
.lesson-nav { display: flex; gap: 10px; }

/* --------------------------------- responsive -------------------------------- */

@media (max-width: 800px) {
  .layout { flex-direction: column; }
  .sidebar { width: 100%; height: auto; position: relative; padding-bottom: 20px; }
  .content { padding: 24px 20px 60px; max-width: 100%; }
  .lesson-footer { flex-direction: column; align-items: stretch; }
}