:root {
  --bg: #0b0b12;
  --surface: #14141f;
  --surface2: #1e1e30;
  --surface3: #2a2a40;
  --border: #2e2e48;
  --text: #e8e8f0;
  --text2: #8888a8;
  --text3: #606080;
  --accent: #6c5ce7;
  --accent2: #a29bfe;
  --green: #00b894;
  --orange: #fdcb6e;
  --red: #d63031;
  --radius: 10px;
  --rad-sm: 6px;
  font-size: 14.5px;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* SCROLLBAR */
::-webkit-scrollbar { width: 5px; height: 5px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 10px; }
::-webkit-scrollbar-thumb:hover { background: var(--surface3); }

#app { display: flex; height: 100vh; overflow: hidden; }

/* ─── SIDEBAR ─── */
#sidebar {
  width: 300px; min-width: 300px;
  background: var(--surface);
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.sidebar-header {
  padding: 1rem 1rem 0.5rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
  color: var(--accent2);
  border-bottom: 1px solid var(--border);
  padding-bottom: 0.75rem;
  margin: 0 0.75rem;
}
.sidebar-header h2 { font-size: 0.95rem; font-weight: 700; color: var(--text); letter-spacing: -0.2px; }

.search-box {
  position: relative;
  margin: 0.6rem 0.75rem;
}
.search-icon { position: absolute; left: 10px; top: 50%; transform: translateY(-50%); color: var(--text3); }
.search-box input {
  width: 100%;
  padding: 0.5rem 0.75rem 0.5rem 2rem;
  border-radius: var(--rad-sm);
  border: 1px solid var(--border);
  background: var(--surface2);
  color: var(--text);
  font-size: 0.78rem;
  outline: none;
  transition: border 0.15s, box-shadow 0.15s;
}
.search-box input:focus { border-color: var(--accent); box-shadow: 0 0 0 2px rgba(108,92,231,0.15); }
.search-box input::placeholder { color: var(--text3); }

#moduleNav { flex: 1; overflow-y: auto; padding: 0 0.5rem 0.75rem; }

.module-group { margin-bottom: 0.15rem; }

.module-header {
  display: flex;
  align-items: center;
  gap: 0.45rem;
  padding: 0.45rem 0.5rem;
  cursor: pointer;
  border-radius: var(--rad-sm);
  transition: background 0.12s;
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text2);
  user-select: none;
}
.module-header:hover { background: var(--surface2); color: var(--text); }
.module-header .arrow {
  font-size: 0.55rem;
  transition: transform 0.2s;
  color: var(--text3);
  flex-shrink: 0;
}
.module-header.open .arrow { transform: rotate(90deg); }
.module-header .mod-num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 20px; height: 20px;
  border-radius: 4px;
  background: var(--surface3);
  font-size: 0.6rem;
  font-weight: 700;
  color: var(--accent2);
  flex-shrink: 0;
}
.module-header .mod-title { flex: 1; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.module-header .mod-check {
  flex-shrink: 0;
  width: 14px; height: 14px;
  border-radius: 50%;
  border: 1.5px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s;
}
.module-header .mod-check.done { background: var(--green); border-color: var(--green); }
.module-header .mod-check svg { opacity: 0; width: 8px; height: 8px; transition: opacity 0.2s; }
.module-header .mod-check.done svg { opacity: 1; }

.module-lessons { max-height: 0; overflow: hidden; transition: max-height 0.25s ease; }
.module-lessons.open { max-height: 2000px; }

.lesson-link {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.35rem 0.5rem 0.35rem 2rem;
  font-size: 0.75rem;
  color: var(--text2);
  cursor: pointer;
  border-radius: var(--rad-sm);
  transition: all 0.1s;
  border-left: 2px solid transparent;
}
.lesson-link:hover { background: var(--surface2); color: var(--text); }
.lesson-link.active {
  background: rgba(108,92,231,0.12);
  color: var(--accent2);
  border-left-color: var(--accent);
}
.lesson-link .check {
  flex-shrink: 0;
  width: 12px; height: 12px;
  border-radius: 50%;
  border: 1.5px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
}
.lesson-link .check.done { background: var(--green); border-color: var(--green); }
.lesson-link .check svg { opacity: 0; width: 7px; height: 7px; }
.lesson-link .check.done svg { opacity: 1; }

.sidebar-footer {
  padding: 0.65rem 0.75rem;
  border-top: 1px solid var(--border);
  font-size: 0.7rem;
  color: var(--text3);
}
.progress-track {
  height: 3px;
  background: var(--surface2);
  border-radius: 4px;
  margin-top: 0.35rem;
  overflow: hidden;
}
#progressFill {
  height: 100%;
  width: 0%;
  background: linear-gradient(90deg, var(--accent), var(--green));
  border-radius: 4px;
  transition: width 0.4s ease;
}

/* ─── MAIN ─── */
#mainContent { flex: 1; overflow-y: auto; padding: 2rem 2.5rem; }

/* ─── WELCOME ─── */
.welcome-screen { display: flex; align-items: center; justify-content: center; min-height: 85vh; }
.welcome-card { text-align: center; max-width: 500px; }
.welcome-logo { opacity: 0.8; }
.welcome-card h1 {
  font-size: 1.65rem;
  font-weight: 800;
  margin-bottom: 0.6rem;
  letter-spacing: -0.3px;
  background: linear-gradient(135deg, var(--accent2), var(--green));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.welcome-subtitle { color: var(--text2); line-height: 1.7; margin-bottom: 1.5rem; font-size: 0.88rem; }
.stats-row { display: flex; gap: 2rem; justify-content: center; margin-bottom: 1.8rem; }
.stat { display: flex; flex-direction: column; align-items: center; }
.stat span { font-size: 1.3rem; font-weight: 700; color: var(--accent2); }
.stat small { font-size: 0.65rem; color: var(--text3); text-transform: uppercase; letter-spacing: 0.8px; margin-top: 0.15rem; }
.welcome-hint { margin-top: 1rem; font-size: 0.72rem; color: var(--text3); }

/* ─── LESSON VIEW ─── */
.lesson-header {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1.2rem;
  flex-wrap: wrap;
}
.btn-back {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  background: none;
  border: none;
  color: var(--text2);
  cursor: pointer;
  font-size: 0.78rem;
  padding: 0.35rem 0.5rem;
  border-radius: var(--rad-sm);
  transition: all 0.15s;
}
.btn-back:hover { background: var(--surface); color: var(--accent2); }

.lesson-breadcrumb {
  flex: 1;
  font-size: 0.72rem;
  color: var(--text3);
  min-width: 100px;
}
.lesson-breadcrumb span { color: var(--text2); }

.lesson-nav { display: flex; align-items: center; gap: 0.3rem; }
.lesson-nav button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 30px; height: 30px;
  border-radius: var(--rad-sm);
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text2);
  cursor: pointer;
  transition: all 0.15s;
}
.lesson-nav button:hover:not(:disabled) { border-color: var(--accent); color: var(--accent2); background: rgba(108,92,231,0.08); }
.lesson-nav button:disabled { opacity: 0.3; cursor: default; }
#lessonCounter { font-size: 0.72rem; color: var(--text3); min-width: 55px; text-align: center; }

.lesson-content {
  animation: fadeIn 0.2s ease;
}

@keyframes fadeIn { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: translateY(0); } }

.lesson-content h1 {
  font-size: 1.5rem;
  font-weight: 700;
  margin-bottom: 0.75rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--border);
  letter-spacing: -0.3px;
}
.lesson-content h2 {
  font-size: 1.1rem;
  font-weight: 600;
  margin: 1.8rem 0 0.6rem;
  color: var(--accent2);
}
.lesson-content h3 {
  font-size: 0.95rem;
  font-weight: 600;
  margin: 1.4rem 0 0.5rem;
}
.lesson-content h4 { font-size: 0.88rem; font-weight: 600; margin: 1rem 0 0.4rem; color: var(--text2); }
.lesson-content p { margin: 0.6rem 0; line-height: 1.7; color: var(--text2); }
.lesson-content ul, .lesson-content ol { margin: 0.5rem 0; padding-left: 1.4rem; line-height: 1.7; color: var(--text2); }
.lesson-content li { margin: 0.25rem 0; }
.lesson-content a { color: var(--accent2); text-decoration: none; }
.lesson-content a:hover { text-decoration: underline; }

.lesson-content pre {
  background: var(--surface2);
  border-radius: var(--radius);
  padding: 1rem 1.2rem;
  overflow-x: auto;
  margin: 0.8rem 0;
  border: 1px solid var(--border);
  font-size: 0.8rem;
  line-height: 1.5;
  position: relative;
}
.lesson-content code {
  font-family: 'SF Mono', 'Fira Code', 'JetBrains Mono', 'Cascadia Code', monospace;
  font-size: 0.8rem;
}
.lesson-content p code, .lesson-content li code {
  background: var(--surface2);
  padding: 0.1rem 0.35rem;
  border-radius: 4px;
  border: 1px solid var(--border);
}
.lesson-content pre code { background: none; padding: 0; border: none; }

.lesson-content table {
  width: 100%;
  border-collapse: collapse;
  margin: 0.8rem 0;
  font-size: 0.8rem;
  border-radius: var(--radius);
  overflow: hidden;
}
.lesson-content th, .lesson-content td {
  padding: 0.5rem 0.75rem;
  border: 1px solid var(--border);
  text-align: left;
}
.lesson-content th { background: var(--surface2); color: var(--text); font-weight: 600; font-size: 0.78rem; text-transform: uppercase; letter-spacing: 0.3px; }
.lesson-content td { color: var(--text2); }

.lesson-content blockquote {
  border-left: 3px solid var(--accent);
  padding: 0.5rem 1rem;
  margin: 0.8rem 0;
  background: var(--surface);
  border-radius: 0 var(--rad-sm) var(--rad-sm) 0;
  color: var(--text2);
  font-style: italic;
}

.lesson-content details {
  margin: 0.8rem 0;
  background: var(--surface);
  border-radius: var(--rad-sm);
  border: 1px solid var(--border);
  overflow: hidden;
}
.lesson-content details summary {
  cursor: pointer;
  font-weight: 600;
  color: var(--accent2);
  padding: 0.6rem 1rem;
  font-size: 0.85rem;
  user-select: none;
}
.lesson-content details summary:hover { background: var(--surface2); }
.lesson-content details[open] summary { border-bottom: 1px solid var(--border); }
.lesson-content details > :not(summary) { padding: 0.6rem 1rem 0.8rem; }

.lesson-content hr { border: none; border-top: 1px solid var(--border); margin: 1.5rem 0; }

.lesson-content img { max-width: 100%; border-radius: var(--radius); margin: 0.8rem 0; border: 1px solid var(--border); }

.lesson-content .learning-objectives {
  background: var(--surface);
  border: 1px solid var(--border);
  border-left: 3px solid var(--accent);
  border-radius: var(--rad-sm);
  padding: 1rem 1.2rem;
  margin: 1rem 0;
}
.lesson-content .learning-objectives p { margin: 0.2rem 0; font-size: 0.85rem; }

.lesson-loading {
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 4rem 2rem;
  color: var(--text3);
  font-size: 0.85rem;
}

.lesson-footer {
  display: flex;
  justify-content: center;
  margin-top: 1.5rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
}

.btn-complete {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.5rem 1.5rem;
  border-radius: var(--rad-sm);
  border: 1px solid var(--green);
  background: transparent;
  color: var(--green);
  cursor: pointer;
  font-size: 0.8rem;
  font-weight: 600;
  transition: all 0.2s;
}
.btn-complete:hover { background: rgba(0,184,148,0.1); }
.btn-complete.done { background: var(--green); color: #fff; border-color: var(--green); }

.btn-primary {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.65rem 2rem;
  border-radius: var(--rad-sm);
  border: none;
  background: linear-gradient(135deg, var(--accent), var(--accent2));
  color: #fff;
  font-size: 0.88rem;
  font-weight: 600;
  cursor: pointer;
  transition: transform 0.12s, box-shadow 0.15s;
}
.btn-primary:hover { transform: translateY(-1px); box-shadow: 0 4px 20px rgba(108,92,231,0.3); }
.btn-primary:active { transform: translateY(0); }

/* EMPTY STATE (search) */
.empty-state { text-align: center; padding: 3rem 1rem; color: var(--text3); font-size: 0.82rem; }

/* ─── RESPONSIVE ─── */
@media (max-width: 768px) {
  #sidebar {
    width: 100%; min-width: unset;
    max-height: 40vh;
    border-right: none;
    border-bottom: 1px solid var(--border);
  }
  #app { flex-direction: column; height: 100vh; }
  #mainContent { padding: 1rem; }
  .welcome-card h1 { font-size: 1.25rem; }
  .lesson-header { flex-direction: column; align-items: flex-start; }
}