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

/* Design tokens live in theme.css (loaded before this file). */

body {
  font-family: var(--font-sans);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
}

/* ===== Top Bar ===== */
.top-bar {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--topbar-h);
  background: var(--color-surface);
  border-bottom: 1px solid var(--color-border);
  display: flex;
  align-items: center;
  padding: 0 1.5rem;
}

.breadcrumb {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.82rem;
}

.breadcrumb-link {
  color: var(--color-primary);
  text-decoration: none;
  font-weight: 500;
}

.breadcrumb-link:hover {
  text-decoration: underline;
}

.breadcrumb-sep {
  color: var(--color-text-muted);
}

.breadcrumb-current {
  color: var(--color-text-secondary);
  font-weight: 500;
}

/* ===== App Layout ===== */
.app-layout {
  display: flex;
  min-height: calc(100vh - var(--topbar-h));
}

/* ===== Sidebar ===== */
.sidebar {
  width: var(--sidebar-w);
  min-width: var(--sidebar-w);
  background: var(--color-sidebar-bg);
  color: var(--color-sidebar-text);
  display: flex;
  flex-direction: column;
  position: sticky;
  top: var(--topbar-h);
  height: calc(100vh - var(--topbar-h));
  overflow-y: auto;
  overflow-x: hidden;
}

.sidebar-header {
  padding: 1.5rem 1.25rem 1rem;
  display: flex;
  align-items: flex-start;
  gap: 0.75rem;
  border-bottom: 1px solid rgba(255,255,255,0.08);
}

.course-icon {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-md);
  background: rgba(13, 148, 136, 0.15);
  color: var(--color-primary-light);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
}

.course-title {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--color-sidebar-active-text);
  letter-spacing: -0.01em;
  line-height: 1.3;
}

.course-subtitle {
  font-size: 0.72rem;
  color: var(--color-sidebar-text-dim);
  margin-top: 0.15rem;
}

/* ===== Progress ===== */
.progress-section {
  padding: 1rem 1.25rem;
  border-bottom: 1px solid rgba(255,255,255,0.08);
}

.progress-bar-container {
  height: 6px;
  background: rgba(255,255,255,0.1);
  border-radius: 99px;
  overflow: hidden;
  margin-bottom: 0.45rem;
}

.progress-bar-fill {
  height: 100%;
  width: 0%;
  background: var(--color-primary-light);
  border-radius: 99px;
  transition: width 0.4s ease;
}

.progress-text {
  font-size: 0.72rem;
  color: var(--color-sidebar-text-dim);
}

/* ===== Mobile lesson toggle ===== */
.mobile-lesson-toggle {
  display: none;
  width: calc(100% - 2.5rem);
  margin: 0.75rem 1.25rem;
  padding: 0.6rem 0.85rem;
  background: var(--color-sidebar-active-bg);
  border: 1px solid rgba(255,255,255,0.12);
  border-radius: var(--radius-sm);
  color: var(--color-sidebar-active-text);
  font-family: var(--font-sans);
  font-size: 0.82rem;
  font-weight: 500;
  cursor: pointer;
  align-items: center;
  justify-content: space-between;
}

.mobile-lesson-toggle svg {
  transition: transform 0.2s;
}

.mobile-lesson-toggle.open svg {
  transform: rotate(180deg);
}

/* ===== Lesson Nav ===== */
.lesson-nav {
  flex: 1;
  overflow-y: auto;
  padding: 0.5rem 0;
}

.nav-group {
  padding: 0.5rem 0;
}

.nav-group-title {
  font-size: 0.65rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--color-sidebar-group);
  padding: 0.5rem 1.25rem 0.35rem;
}

.nav-list {
  list-style: none;
}

.nav-item {
  position: relative;
}

.nav-item a {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  padding: 0.55rem 1.25rem;
  text-decoration: none;
  color: var(--color-sidebar-text);
  font-size: 0.82rem;
  font-weight: 400;
  transition: background 0.15s, color 0.15s;
  cursor: pointer;
  border-left: 3px solid transparent;
}

.nav-item a:hover {
  background: var(--color-sidebar-hover-bg);
  color: var(--color-sidebar-active-text);
}

.nav-item.active a {
  background: var(--color-sidebar-active-bg);
  color: var(--color-sidebar-active-text);
  font-weight: 600;
  border-left-color: var(--color-primary-light);
}

.nav-item.completed a {
  color: var(--color-sidebar-text-dim);
}

.nav-lesson-num {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.68rem;
  font-weight: 600;
  flex-shrink: 0;
  background: rgba(255,255,255,0.08);
  color: var(--color-sidebar-text);
  transition: background 0.2s, color 0.2s;
}

.nav-item.active .nav-lesson-num {
  background: var(--color-primary);
  color: #fff;
}

.nav-item.completed .nav-lesson-num {
  background: var(--color-success);
  color: #fff;
}

.nav-item.completed .nav-lesson-num .num-text { display: none; }
.nav-item .nav-lesson-num .check-icon { display: none; }
.nav-item.completed .nav-lesson-num .check-icon { display: block; }

.nav-lesson-title {
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* ===== Sidebar Footer ===== */
.sidebar-footer {
  padding: 0.75rem 1.25rem;
  border-top: 1px solid rgba(255,255,255,0.08);
}

.reset-btn {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  background: none;
  border: none;
  color: var(--color-sidebar-text-dim);
  font-family: var(--font-sans);
  font-size: 0.72rem;
  cursor: pointer;
  padding: 0.35rem 0;
  transition: color 0.15s;
}

.reset-btn:hover {
  color: var(--color-sidebar-active-text);
}

/* ===== Main Content ===== */
.main-content {
  flex: 1;
  min-width: 0;
  max-width: 820px;
  padding: 2rem 3rem 4rem;
  margin: 0 auto;
}

/* ===== Completion Banner ===== */
.completion-banner {
  display: flex;
  align-items: center;
  gap: 0.85rem;
  padding: 1rem 1.25rem;
  background: var(--color-success-surface);
  border: 1px solid rgba(16, 185, 129, 0.2);
  border-radius: var(--radius-md);
  margin-bottom: 1.5rem;
  color: var(--color-text);
}

.completion-banner .completion-icon {
  color: var(--color-success);
  flex-shrink: 0;
}

.completion-banner strong {
  font-size: 0.92rem;
}

.completion-banner p {
  font-size: 0.82rem;
  color: var(--color-text-secondary);
  margin-top: 0.15rem;
}

.completion-banner a {
  color: var(--color-primary);
  text-decoration: none;
  font-weight: 500;
}

.completion-banner a:hover {
  text-decoration: underline;
}

/* ===== Lesson Header ===== */
.lesson-header {
  margin-bottom: 1.75rem;
  padding-bottom: 1.25rem;
  border-bottom: 1px solid var(--color-border);
}

.lesson-number {
  display: inline-block;
  font-size: 0.7rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--color-primary);
  margin-bottom: 0.35rem;
}

.lesson-title {
  font-size: 1.6rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--color-text);
  line-height: 1.25;
}

/* ===== Lesson Body (rendered markdown) ===== */
.lesson-body {
  font-size: 0.92rem;
  line-height: 1.75;
  color: var(--color-text-secondary);
}

.lesson-body h2 {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--color-text);
  margin-top: 2.25rem;
  margin-bottom: 0.75rem;
  letter-spacing: -0.01em;
}

.lesson-body h3 {
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--color-text);
  margin-top: 1.75rem;
  margin-bottom: 0.55rem;
}

.lesson-body h4 {
  font-size: 0.92rem;
  font-weight: 600;
  color: var(--color-text);
  margin-top: 1.25rem;
  margin-bottom: 0.4rem;
}

.lesson-body p {
  margin-bottom: 1rem;
}

.lesson-body ul, .lesson-body ol {
  margin-bottom: 1rem;
  padding-left: 1.5rem;
}

.lesson-body li {
  margin-bottom: 0.35rem;
}

.lesson-body li > ul, .lesson-body li > ol {
  margin-top: 0.35rem;
  margin-bottom: 0;
}

.lesson-body strong {
  color: var(--color-text);
  font-weight: 600;
}

.lesson-body a {
  color: var(--color-primary);
  text-decoration: none;
}

.lesson-body a:hover {
  text-decoration: underline;
}

.lesson-body code {
  font-family: var(--font-mono);
  font-size: 0.82em;
  background: var(--color-bg);
  border: 1px solid var(--color-border-light);
  padding: 0.15em 0.4em;
  border-radius: 4px;
  color: var(--color-text);
}

.lesson-body pre {
  background: var(--color-sidebar-bg);
  color: #e2e5ea;
  padding: 1.25rem 1.5rem;
  border-radius: var(--radius-md);
  overflow-x: auto;
  margin-bottom: 1.25rem;
  font-size: 0.8rem;
  line-height: 1.6;
}

.lesson-body pre code {
  background: none;
  border: none;
  padding: 0;
  color: inherit;
  font-size: inherit;
}

.lesson-body table {
  width: 100%;
  border-collapse: collapse;
  margin-bottom: 1.25rem;
  font-size: 0.85rem;
}

.lesson-body th {
  background: var(--color-bg);
  font-weight: 600;
  color: var(--color-text);
  text-align: left;
  padding: 0.6rem 0.85rem;
  border: 1px solid var(--color-border);
}

.lesson-body td {
  padding: 0.55rem 0.85rem;
  border: 1px solid var(--color-border-light);
  vertical-align: top;
}

.lesson-body tr:hover td {
  background: var(--color-primary-surface);
}

.lesson-body blockquote {
  border-left: 3px solid var(--color-primary);
  padding: 0.75rem 1rem;
  margin-bottom: 1rem;
  background: var(--color-primary-surface);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  color: var(--color-text-secondary);
}

.lesson-body blockquote p:last-child {
  margin-bottom: 0;
}

.lesson-body hr {
  border: none;
  border-top: 1px solid var(--color-border);
  margin: 2rem 0;
}

/* Lesson video embed */
.lesson-video {
  position: relative;
  width: 100%;
  aspect-ratio: 16 / 9;
  margin-bottom: 2rem;
  border-radius: var(--radius-md);
  overflow: hidden;
  background: var(--color-sidebar-bg);
}

.lesson-video iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  border: none;
}

/* Key Takeaways styled block */
.lesson-body .key-takeaways {
  background: var(--color-primary-surface);
  border: 1px solid rgba(13, 148, 136, 0.15);
  border-radius: var(--radius-md);
  padding: 1.25rem 1.5rem;
  margin-top: 1.5rem;
  margin-bottom: 1rem;
}

.lesson-body .key-takeaways h2 {
  font-size: 0.95rem;
  color: var(--color-primary);
  margin-top: 0;
  margin-bottom: 0.65rem;
  display: flex;
  align-items: center;
  gap: 0.45rem;
}

.lesson-body .key-takeaways ul {
  margin-bottom: 0;
}

.lesson-body .key-takeaways li {
  font-size: 0.85rem;
}

/* ===== Loading ===== */
.loading-spinner {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 4rem 0;
  gap: 1rem;
  color: var(--color-text-muted);
  font-size: 0.85rem;
}

.spinner {
  width: 28px;
  height: 28px;
  border: 3px solid var(--color-border);
  border-top-color: var(--color-primary);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* ===== Error ===== */
.error-state {
  text-align: center;
  padding: 3rem 1rem;
  color: var(--color-text-muted);
}

.error-state p {
  margin-bottom: 1rem;
  font-size: 0.9rem;
}

.error-state button {
  background: var(--color-primary);
  color: #fff;
  border: none;
  padding: 0.5rem 1.25rem;
  border-radius: var(--radius-sm);
  font-family: var(--font-sans);
  font-size: 0.82rem;
  font-weight: 500;
  cursor: pointer;
}

.error-state button:hover {
  background: var(--color-primary-light);
}

/* ===== Quiz Section ===== */
.quiz-section {
  margin-top: 2.5rem;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
}

.quiz-header {
  display: flex;
  align-items: center;
  gap: 0.55rem;
  margin-bottom: 1.25rem;
  color: var(--color-primary);
}

.quiz-header h3 {
  font-size: 1rem;
  font-weight: 700;
  color: var(--color-text);
}

.quiz-question {
  margin-bottom: 1.5rem;
}

.quiz-question:last-of-type {
  margin-bottom: 0;
}

.quiz-question-text {
  font-size: 0.92rem;
  font-weight: 600;
  color: var(--color-text);
  margin-bottom: 0.75rem;
  line-height: 1.45;
}

.quiz-question-number {
  font-size: 0.7rem;
  color: var(--color-text-muted);
  margin-bottom: 0.35rem;
  font-weight: 500;
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 0.45rem;
}

.quiz-option {
  display: flex;
  align-items: flex-start;
  gap: 0.65rem;
  padding: 0.65rem 0.85rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: border-color 0.15s, background 0.15s;
  font-size: 0.85rem;
  color: var(--color-text-secondary);
  line-height: 1.45;
}

.quiz-option:hover {
  border-color: var(--color-primary);
  background: var(--color-primary-surface);
}

.quiz-option.selected {
  border-color: var(--color-primary);
  background: var(--color-primary-dim);
  color: var(--color-text);
}

.quiz-option.correct {
  border-color: var(--color-success);
  background: var(--color-success-dim);
  color: var(--color-text);
}

.quiz-option.incorrect {
  border-color: var(--color-danger);
  background: var(--color-danger-dim);
  color: var(--color-text);
  opacity: 0.7;
}

.quiz-option input[type="radio"] {
  appearance: none;
  -webkit-appearance: none;
  width: 18px;
  height: 18px;
  border: 2px solid var(--color-border);
  border-radius: 50%;
  flex-shrink: 0;
  margin-top: 1px;
  position: relative;
  transition: border-color 0.15s;
}

.quiz-option.selected input[type="radio"] {
  border-color: var(--color-primary);
}

.quiz-option.selected input[type="radio"]::after {
  content: '';
  position: absolute;
  top: 3px;
  left: 3px;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--color-primary);
}

.quiz-option.correct input[type="radio"] {
  border-color: var(--color-success);
}

.quiz-option.correct input[type="radio"]::after {
  background: var(--color-success);
}

.quiz-option.disabled {
  pointer-events: none;
}

/* ===== Quiz Actions & Feedback ===== */
.quiz-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-top: 1.25rem;
}

.btn {
  font-family: var(--font-sans);
  font-size: 0.85rem;
  font-weight: 600;
  padding: 0.6rem 1.5rem;
  border-radius: var(--radius-sm);
  border: none;
  cursor: pointer;
  transition: background 0.15s, opacity 0.15s;
}

.btn:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

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

.btn-primary:hover:not(:disabled) {
  background: var(--color-primary-light);
}

.btn-secondary {
  background: var(--color-bg);
  color: var(--color-text);
  border: 1px solid var(--color-border);
}

.btn-secondary:hover {
  background: var(--color-border-light);
}

.quiz-feedback {
  margin-top: 1rem;
  padding: 0.75rem 1rem;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  line-height: 1.5;
}

.quiz-feedback.success {
  background: var(--color-success-dim);
  color: #047857;
  border: 1px solid rgba(16, 185, 129, 0.2);
}

.quiz-feedback.error {
  background: var(--color-danger-dim);
  color: #b91c1c;
  border: 1px solid rgba(239, 68, 68, 0.2);
}

/* ===== Completed Badge ===== */
.completed-badge {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin-top: 1.5rem;
  padding: 0.65rem 1rem;
  background: var(--color-success-surface);
  border: 1px solid rgba(16, 185, 129, 0.2);
  border-radius: var(--radius-sm);
  color: var(--color-success);
  font-size: 0.85rem;
  font-weight: 600;
}

/* ===== Responsive ===== */
@media (max-width: 1100px) {
  .main-content {
    padding: 1.5rem 2rem 3rem;
  }
}

@media (max-width: 900px) {
  .sidebar {
    position: fixed;
    top: var(--topbar-h);
    left: 0;
    right: 0;
    width: 100%;
    min-width: 100%;
    height: auto;
    max-height: none;
    z-index: 90;
    overflow: visible;
  }

  .sidebar-header {
    display: none;
  }

  .mobile-lesson-toggle {
    display: flex;
  }

  .lesson-nav {
    display: none;
    max-height: 60vh;
    overflow-y: auto;
    border-top: 1px solid rgba(255,255,255,0.08);
  }

  .lesson-nav.open {
    display: block;
  }

  .sidebar-footer {
    display: none;
  }

  .app-layout {
    flex-direction: column;
  }

  .main-content {
    padding: 1.25rem 1.25rem 3rem;
    max-width: 100%;
  }

  .lesson-title {
    font-size: 1.3rem;
  }
}

@media (max-width: 480px) {
  .main-content {
    padding: 1rem 1rem 2.5rem;
  }

  .lesson-body pre {
    padding: 0.85rem 1rem;
    font-size: 0.72rem;
  }

  .lesson-body table {
    font-size: 0.78rem;
  }

  .quiz-section {
    padding: 1rem;
  }
}