@import url('https://fonts.googleapis.com/css2?family=IBM+Plex+Sans:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500&family=Noto+Sans+Bengali:wght@400;500;600;700&family=Source+Serif+4:ital,opsz,wght@0,8..60,400;0,8..60,600;1,8..60,400&display=swap');

:root {
  --font-ui: 'IBM Plex Sans', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-serif: 'Source Serif 4', Georgia, serif;
  --font-mono: 'JetBrains Mono', monospace;
  --font-bn: 'Noto Sans Bengali', sans-serif;

  --bg: #ffffff;
  --bg-subtle: #f8fafc;
  --bg-card: #ffffff;
  --bg-sidebar: #f8fafc;
  --border: #e2e8f0;
  --border-strong: #cbd5e1;
  --border-focus: #2563eb;

  --text-main: #0f172a;
  --text-secondary: #475569;
  --text-muted: #64748b;

  --accent: #2563eb;
  --accent-hover: #1d4ed8;
  --accent-contrast: #ffffff;

  --badge-bg: #f1f5f9;
  --badge-text: #334155;

  --alert-success-bg: #f0fdf4;
  --alert-success-text: #166534;
  --alert-success-border: #bbf7d0;

  --alert-error-bg: #fef2f2;
  --alert-error-text: #991b1b;
  --alert-error-border: #fecaca;

  --alert-info-bg: #f0f9ff;
  --alert-info-text: #075985;
  --alert-info-border: #bae6fd;

  --radius: 4px;
}

[data-theme="dark"] {
  --bg: #0b0f19;
  --bg-subtle: #111827;
  --bg-card: #151d30;
  --bg-sidebar: #0e1424;
  --border: #243049;
  --border-strong: #334155;
  --border-focus: #3b82f6;

  --text-main: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;

  --accent: #3b82f6;
  --accent-hover: #60a5fa;
  --accent-contrast: #0f172a;

  --badge-bg: #1e293b;
  --badge-text: #cbd5e1;

  --alert-success-bg: #052e16;
  --alert-success-text: #86efac;
  --alert-success-border: #166534;

  --alert-error-bg: #450a0a;
  --alert-error-text: #fca5a5;
  --alert-error-border: #991b1b;

  --alert-info-bg: #082f49;
  --alert-info-text: #7dd3fc;
  --alert-info-border: #0369a1;
}

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

html {
  font-size: 15px;
  background-color: var(--bg);
  color: var(--text-main);
  font-family: var(--font-ui);
  line-height: 1.5;
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
}

body {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  background-color: var(--bg);
  color: var(--text-main);
}

[lang="bn"] body {
  font-family: var(--font-bn), var(--font-ui);
}

a {
  color: var(--accent);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

code, pre {
  font-family: var(--font-mono);
  font-size: 0.9em;
}

/* Top Header */
.top-header {
  border-bottom: 1px solid var(--border);
  background-color: var(--bg);
  height: 52px;
  display: flex;
  align-items: center;
  position: sticky;
  top: 0;
  z-index: 40;
}

.header-container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 16px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.site-brand {
  display: inline-flex;
  align-items: center;
  text-decoration: none;
  line-height: 1;
}

.site-logo-img {
  height: 38px;
  width: auto;
  max-width: 160px;
  object-fit: contain;
  display: block;
  border-radius: 8px;
  transition: transform 0.15s ease, opacity 0.15s ease;
}

.site-brand:hover {
  text-decoration: none;
}

.site-brand:hover .site-logo-img {
  transform: scale(1.03);
  opacity: 0.95;
}

.brand-icon {
  width: 20px;
  height: 20px;
  fill: currentColor;
  color: var(--accent);
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 16px;
  list-style: none;
}

.nav-links a {
  color: var(--text-secondary);
  font-size: 14px;
  font-weight: 500;
}

.nav-links a:hover, .nav-links a.active {
  color: var(--text-main);
  text-decoration: none;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 12px;
}

/* Buttons */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  font-family: var(--font-ui);
  font-size: 13.5px;
  font-weight: 500;
  line-height: 1;
  padding: 8px 14px;
  border-radius: var(--radius);
  border: 1px solid transparent;
  cursor: pointer;
  background-color: transparent;
  color: var(--text-main);
  text-decoration: none;
  transition: background-color 0.15s ease, border-color 0.15s ease;
  white-space: nowrap;
}

.btn:hover {
  text-decoration: none;
}

.btn-primary {
  background-color: var(--accent);
  color: var(--accent-contrast);
  border-color: var(--accent);
}

.btn-primary:hover {
  background-color: var(--accent-hover);
  border-color: var(--accent-hover);
}

.btn-outline {
  border-color: var(--border);
  color: var(--text-main);
  background-color: var(--bg);
}

.btn-outline:hover {
  background-color: var(--bg-subtle);
  border-color: var(--border-strong);
}

.btn-danger {
  background-color: var(--alert-error-bg);
  border-color: var(--alert-error-border);
  color: var(--alert-error-text);
}

.btn-sm {
  padding: 5px 10px;
  font-size: 12px;
}

.btn-icon {
  padding: 6px;
  border: 1px solid var(--border);
  background-color: var(--bg);
  border-radius: var(--radius);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  color: var(--text-secondary);
}

.btn-icon:hover {
  color: var(--text-main);
  border-color: var(--border-strong);
}

/* Layout Containers */
.main-wrapper {
  flex: 1;
  display: flex;
  flex-direction: column;
}

.content-container {
  max-width: 1200px;
  width: 100%;
  margin: 0 auto;
  padding: 24px 16px;
  flex: 1;
}

.narrow-container {
  max-width: 460px;
  width: 100%;
  margin: 48px auto;
  padding: 0 16px;
}

/* Cards & Panels */
.card {
  background-color: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
}

.card-header {
  border-bottom: 1px solid var(--border);
  padding-bottom: 12px;
  margin-bottom: 16px;
}

.card-title {
  font-size: 16px;
  font-weight: 600;
  color: var(--text-main);
  margin: 0;
}

.card-subtitle {
  font-size: 13px;
  color: var(--text-muted);
  margin-top: 4px;
}

/* Forms */
.form-group {
  margin-bottom: 16px;
}

.form-label {
  display: block;
  font-size: 13px;
  font-weight: 500;
  color: var(--text-main);
  margin-bottom: 6px;
}

.form-input, .form-select, .form-textarea, .form-control {
  width: 100%;
  padding: 8px 10px;
  font-size: 14px;
  font-family: var(--font-ui);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background-color: var(--bg);
  color: var(--text-main);
  outline: none;
}

.form-input:focus, .form-select:focus, .form-textarea:focus, .form-control:focus {
  border-color: var(--border-focus);
}

.form-hint {
  font-size: 12px;
  color: var(--text-muted);
  margin-top: 4px;
}

/* Alerts */
.alert {
  padding: 10px 14px;
  border-radius: var(--radius);
  font-size: 13px;
  margin-bottom: 16px;
  border: 1px solid transparent;
  display: flex;
  align-items: flex-start;
  gap: 8px;
}

.alert-success {
  background-color: var(--alert-success-bg);
  color: var(--alert-success-text);
  border-color: var(--alert-success-border);
}

.alert-error {
  background-color: var(--alert-error-bg);
  color: var(--alert-error-text);
  border-color: var(--alert-error-border);
}

.alert-info {
  background-color: var(--alert-info-bg);
  color: var(--alert-info-text);
  border-color: var(--alert-info-border);
}

/* Tables */
.table-responsive {
  width: 100%;
  overflow-x: auto;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  margin: 16px 0;
}

.data-table {
  width: 100%;
  border-collapse: collapse;
  text-align: left;
  font-size: 13.5px;
}

.data-table th {
  background-color: var(--bg-subtle);
  color: var(--text-secondary);
  font-weight: 600;
  padding: 10px 12px;
  border-bottom: 1px solid var(--border);
  white-space: nowrap;
}

.data-table td {
  padding: 10px 12px;
  border-bottom: 1px solid var(--border);
  color: var(--text-main);
}

.data-table tr:last-child td {
  border-bottom: none;
}

.data-table tr:hover td {
  background-color: var(--bg-subtle);
}

/* Badges */
.badge {
  display: inline-block;
  padding: 2px 7px;
  font-size: 11px;
  font-weight: 600;
  border-radius: 3px;
  background-color: var(--badge-bg);
  color: var(--badge-text);
  border: 1px solid var(--border);
  text-transform: uppercase;
  letter-spacing: 0.03em;
}

.badge-success {
  background-color: var(--alert-success-bg);
  color: var(--alert-success-text);
  border-color: var(--alert-success-border);
}

.badge-warning {
  background-color: #fefce8;
  color: #854d0e;
  border-color: #fef08a;
}

[data-theme="dark"] .badge-warning {
  background-color: #422006;
  color: #fef08a;
  border-color: #713f12;
}

/* Footer */
.site-footer {
  border-top: 1px solid var(--border);
  padding: 16px 0;
  margin-top: auto;
  background-color: var(--bg);
  font-size: 13px;
  color: var(--text-muted);
}

.footer-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 16px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

/* SVG icons helper */
.icon {
  width: 16px;
  height: 16px;
  fill: currentColor;
  flex-shrink: 0;
}

/* Grid helper */
.grid-cols-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 16px;
}

@media (max-width: 768px) {
  .grid-cols-3 {
    grid-template-columns: 1fr;
  }
}

/* --- W3Schools-style Lesson Reader Layout --- */
.lesson-layout {
  display: flex;
  margin: -24px -16px;
  min-height: calc(100vh - 52px);
}

.lesson-sidebar {
  width: 290px;
  background-color: var(--bg-sidebar);
  border-right: 1px solid var(--border);
  flex-shrink: 0;
  display: flex;
  flex-direction: column;
  position: sticky;
  top: 52px;
  height: calc(100vh - 52px);
  overflow-y: auto;
}

.lesson-sidebar-header {
  padding: 16px;
  border-bottom: 1px solid var(--border);
  background-color: var(--bg-sidebar);
}

.lesson-sidebar-title {
  font-size: 14px;
  font-weight: 700;
  color: var(--text-main);
  margin-bottom: 4px;
}

.lesson-tree {
  padding: 8px 0;
}

.lesson-chapter-group {
  margin-bottom: 8px;
}

.lesson-chapter-title {
  padding: 8px 16px 4px 16px;
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--text-muted);
}

.lesson-tree-link {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 7px 16px;
  font-size: 13.5px;
  color: var(--text-secondary);
  text-decoration: none;
  border-left: 2px solid transparent;
}

.lesson-tree-link:hover {
  background-color: var(--bg);
  color: var(--text-main);
  text-decoration: none;
}

.lesson-tree-link.active {
  background-color: var(--bg);
  color: var(--accent);
  font-weight: 600;
  border-left-color: var(--accent);
}

.lesson-check-icon {
  width: 14px;
  height: 14px;
  color: #16a34a;
  flex-shrink: 0;
}

/* Reader Main Content */
.lesson-main {
  flex: 1;
  min-width: 0;
  padding: 32px 48px;
  max-width: 860px;
}

.lesson-breadcrumb {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 12.5px;
  color: var(--text-muted);
  margin-bottom: 16px;
}

.lesson-title-main {
  font-size: 28px;
  font-weight: 700;
  color: var(--text-main);
  letter-spacing: -0.02em;
  margin-bottom: 8px;
  line-height: 1.25;
}

.lesson-meta-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--border);
  margin-bottom: 24px;
  font-size: 12.5px;
  color: var(--text-muted);
}

/* Lesson Body Typography (Source Serif 4) */
.lesson-body {
  font-family: var(--font-serif);
  font-size: 17px;
  line-height: 1.75;
  color: var(--text-main);
}

.lesson-body p.lesson-paragraph {
  margin-bottom: 20px;
}

.lesson-heading {
  font-family: var(--font-ui);
  font-weight: 700;
  color: var(--text-main);
  margin-top: 36px;
  margin-bottom: 14px;
  scroll-margin-top: 70px;
}

h2.lesson-heading {
  font-size: 20px;
  border-bottom: 1px solid var(--border);
  padding-bottom: 6px;
}

h3.lesson-heading {
  font-size: 16px;
}

.heading-anchor {
  color: var(--border-strong);
  text-decoration: none;
  font-size: 0.8em;
  margin-left: 4px;
  visibility: hidden;
}

.lesson-heading:hover .heading-anchor {
  visibility: visible;
}

.lesson-list {
  margin-bottom: 20px;
  padding-left: 24px;
}

.lesson-list li {
  margin-bottom: 6px;
}

.lesson-blockquote {
  border-left: 3px solid var(--border-strong);
  padding-left: 16px;
  margin: 20px 0;
  color: var(--text-secondary);
  font-style: italic;
}

.inline-code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  background-color: var(--bg-subtle);
  border: 1px solid var(--border);
  padding: 2px 5px;
  border-radius: var(--radius);
  color: var(--text-main);
}

/* Lesson Tables (Markdown & AI Output) */
.lesson-table {
  width: 100%;
  border-collapse: collapse;
  font-family: var(--font-ui);
  font-size: 13.5px;
  line-height: 1.5;
  text-align: left;
  background-color: var(--bg);
}

.lesson-table th {
  background-color: var(--bg-subtle);
  color: var(--text-main);
  font-weight: 600;
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  padding: 10px 14px;
  border-bottom: 1px solid var(--border);
  border-right: 1px solid var(--border);
}

.lesson-table th:last-child {
  border-right: none;
}

.lesson-table td {
  padding: 10px 14px;
  color: var(--text-main);
  border-bottom: 1px solid var(--border);
  border-right: 1px solid var(--border);
  vertical-align: top;
}

.lesson-table td:last-child {
  border-right: none;
}

.lesson-table tbody tr:last-child td {
  border-bottom: none;
}

.lesson-table tbody tr:hover {
  background-color: var(--bg-subtle);
}

/* Code Blocks */
.code-block-wrapper {
  margin: 24px 0;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background-color: var(--bg-subtle);
  overflow: hidden;
}

.code-block-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 6px 12px;
  background-color: var(--bg);
  border-bottom: 1px solid var(--border);
  gap: 8px;
}

.code-lang-label {
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 600;
  color: var(--text-muted);
}

.code-block-wrapper pre {
  margin: 0;
  padding: 14px 16px;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 13.5px;
  line-height: 1.6;
  background-color: var(--bg-subtle);
  color: var(--text-main);
}

/* AI Assistant & Hint Output Typography (Strictly Scaled) */
.ai-output-body {
  font-family: var(--font-serif);
  font-size: 14.5px;
  line-height: 1.65;
  color: var(--text-main);
}

.ai-output-body .lesson-paragraph {
  margin-bottom: 12px;
}

.ai-output-body .lesson-heading {
  margin-top: 18px;
  margin-bottom: 8px;
  font-size: 15px;
}

.ai-output-body h3.lesson-heading {
  font-size: 15px;
}

.ai-output-body h4.lesson-heading {
  font-size: 13.5px;
}

.ai-output-body .code-block-wrapper {
  margin: 14px 0;
}

.ai-output-body .code-block-wrapper pre {
  padding: 10px 12px;
  font-size: 12.5px;
}

.ai-output-body .table-responsive {
  margin: 14px 0;
}

.ai-output-body .lesson-table {
  font-size: 12.5px;
}

.ai-output-body .lesson-table th,
.ai-output-body .lesson-table td {
  padding: 7px 10px;
}

.ai-output-body .lesson-list {
  margin-bottom: 12px;
  padding-left: 20px;
}

.ai-output-body .lesson-list li {
  margin-bottom: 4px;
}

/* TOC Aside */
.lesson-toc {
  width: 220px;
  flex-shrink: 0;
  padding: 32px 16px;
  position: sticky;
  top: 52px;
  height: calc(100vh - 52px);
  overflow-y: auto;
  display: block;
}

.lesson-toc-title {
  font-size: 12px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-muted);
  margin-bottom: 12px;
}

.lesson-toc-list {
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.lesson-toc-list a {
  font-size: 13px;
  color: var(--text-secondary);
  display: block;
  line-height: 1.4;
}

.lesson-toc-list a:hover {
  color: var(--text-main);
}

/* Lesson Navigation Bar */
.lesson-nav-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}

/* Try-It Sandboxed Runner Modal */
.try-it-modal {
  display: none;
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  inset: 0;
  background-color: rgba(0, 0, 0, 0.7);
  z-index: 100;
  align-items: center;
  justify-content: center;
  padding: 24px;
}

.try-it-modal.open {
  display: flex;
}

.try-it-container {
  width: 95%;
  max-width: 1100px;
  height: 85vh;
  background-color: var(--bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  display: flex;
  flex-direction: column;
  overflow: hidden;
}

.try-it-header {
  height: 48px;
  padding: 0 16px;
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  background-color: var(--bg-subtle);
}

.try-it-split {
  flex: 1;
  display: grid;
  grid-template-columns: 1fr 1fr;
  min-height: 0;
}

.try-it-code-editor {
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
}

.try-it-textarea {
  flex: 1;
  width: 100%;
  border: none;
  padding: 16px;
  font-family: var(--font-mono);
  font-size: 13.5px;
  line-height: 1.5;
  background-color: var(--bg);
  color: var(--text-main);
  resize: none;
  outline: none;
}

.try-it-preview-wrapper {
  background-color: #ffffff;
  display: flex;
  flex-direction: column;
}

.try-it-iframe {
  flex: 1;
  width: 100%;
  height: 100%;
  border: none;
  background-color: #ffffff;
}

@media (max-width: 1100px) {
  .lesson-toc {
    display: none;
  }
}

@media (max-width: 800px) {
  .lesson-sidebar {
    display: none;
  }
  .lesson-main {
    padding: 20px 16px;
  }
  .try-it-split {
    grid-template-columns: 1fr;
    grid-template-rows: 1fr 1fr;
  }
}

@keyframes navSlideDown {
  from {
    opacity: 0;
    transform: translateY(-8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

/* ==========================================================
   COMPREHENSIVE RESPONSIVE DESIGN SYSTEM
   ========================================================== */

/* Mobile Menu Button - Hidden on desktop */
.mobile-menu-btn {
  display: none;
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-main);
  padding: 5px;
  border-radius: var(--radius);
  cursor: pointer;
  align-items: center;
  justify-content: center;
  line-height: 1;
}

.mobile-menu-btn:hover {
  background-color: var(--bg-subtle);
  border-color: var(--border-strong);
}

.auth-buttons-desktop {
  display: flex;
  align-items: center;
  gap: 8px;
}

.mobile-nav-auth {
  display: none;
}

/* Tablet & Mobile Screens (<= 900px) */
@media (max-width: 900px) {
  /* Hide the cramped auth buttons from the mobile top bar */
  .auth-buttons-desktop {
    display: none !important;
  }

  .mobile-menu-btn {
    display: inline-flex;
  }

  .site-nav {
    display: none;
    position: absolute;
    top: 50px;
    left: 0;
    right: 0;
    background-color: var(--bg);
    border-bottom: 1px solid var(--border);
    box-shadow: 0 16px 28px rgba(0, 0, 0, 0.2);
    padding: 12px 16px 16px;
    z-index: 50;
    animation: navSlideDown 0.2s cubic-bezier(0.16, 1, 0.3, 1);
  }

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

  /* Show the auth section inside the mobile dropdown */
  .mobile-nav-auth {
    display: block;
    margin-top: 10px;
    padding-top: 10px;
    border-top: 1px solid var(--border);
  }

  .mobile-user-info {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 4px 6px;
    font-size: 13.5px;
    font-weight: 600;
  }



  .nav-links {
    flex-direction: column;
    align-items: stretch;
    gap: 4px;
    width: 100%;
  }

  .nav-links li a {
    display: block;
    padding: 10px 14px;
    font-size: 14.5px;
    font-weight: 600;
    border-radius: var(--radius);
    color: var(--text-main);
    transition: background 0.15s ease;
  }

  .nav-links li a:hover,
  .nav-links li a.active {
    background-color: var(--bg-subtle);
    color: var(--accent);
  }

  .header-actions {
    gap: 6px;
    flex-shrink: 0;
  }
}

/* Small Smartphone Screens (<= 640px) */
@media (max-width: 640px) {
  html {
    font-size: 14px;
  }

  .top-header {
    height: 50px;
  }

  .header-container {
    padding: 0 12px;
  }

  .site-brand span {
    font-size: 15px;
  }

  .main-wrapper {
    padding: 14px 10px;
  }

  .content-container {
    padding: 0;
    max-width: 100%;
  }

  /* Footer responsiveness */
  .footer-container {
    flex-direction: column;
    gap: 6px;
    text-align: center;
    padding: 0 12px;
  }

  /* Compact controls on mobile */
  .auth-buttons-desktop .btn {
    padding: 5px 9px;
    font-size: 11.5px;
  }

  /* Cards & Forms on mobile */
  .card {
    padding: 14px 16px;
  }

  .form-group {
    margin-bottom: 14px;
  }

  .btn {
    min-height: 36px;
  }

  /* Responsive Tables */
  .table-responsive {
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
    width: 100%;
    margin-bottom: 12px;
  }

  .data-table th,
  .data-table td {
    padding: 8px 10px;
    font-size: 12px;
  }
}