:root {
  --bg-primary: #0d1117;
  --bg-secondary: #161b22;
  --bg-tertiary: #21262d;
  --accent-blue: #58a6ff;
  --accent-green: #3fb950;
  --accent-purple: #bc8cff;
  --accent-yellow: #e3b341;
  --text-primary: #e6edf3;
  --text-secondary: #8b949e;
  --border-color: #30363d;
  --hover-color: #2c333a;
  --sidebar-width: 320px;
}

/* Reset and general rules */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  background: var(--bg-primary);
  color: var(--text-primary);
  font-family: 'Open Sans', sans-serif;
  line-height: 1.6;
  display: flex;
  gap: 25px;
  padding: 0;
  margin: 0;
  min-height: 100vh;
  position: relative;
}

/* Scrollbar styling */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--bg-secondary);
}

::-webkit-scrollbar-thumb {
  background: var(--border-color);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--text-secondary);
}


/* Sidebar styling */
.sidebar {
  background-color: var(--bg-secondary);
  width: var(--sidebar-width);
  height: calc(100vh - 130px);
  position: fixed;
  top: 130px;
  left: 0;
  overflow-y: auto;
  transition: all 0.3s ease;
  padding: 20px;
  border-right: 1px solid var(--border-color);
}

.sidebar h2 {
  font-size: 1.4rem;
  margin-bottom: 20px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--border-color);
  color: var(--accent-blue);
  display: flex;
  align-items: center;
}

.sidebar h2 i {
  margin-right: 10px;
}

/* TOC styling */
.toc {
  margin-left: 0 !important;
}

.toc ul {
  list-style-type: none;
  padding-left: 0;
}

.toc > ul > li {
  margin-bottom: 15px;
}

.toc > ul > li > a {
  font-weight: 600;
  color: var(--text-primary);
  font-size: 1rem;
}

.toc ul ul {
  padding-left: 20px;
  margin-top: 8px;
}

.toc li {
  margin: 8px 0;
  position: relative;
}

.toc a {
  color: var(--text-secondary);
  text-decoration: none;
  display: block;
  padding: 5px 10px;
  border-radius: 4px;
  transition: all 0.2s ease;
  font-size: 0.95rem;
}

.toc a:hover {
  color: var(--text-primary);
  background-color: var(--hover-color);
}

.toc .active {
  color: var(--accent-blue);
  background-color: rgba(88, 166, 255, 0.2);
  border-left: 3px solid var(--accent-blue);
  font-weight: bold;
  padding-left: 12px;
  transform: translateX(3px);
  transition: all 0.3s ease;
}

.toc .duration {
  font-size: 0.8rem;
  color: var(--text-secondary);
  margin-left: 5px;
  opacity: 0.8;
}

/* Content area styling */
.content-area {
  margin-left: var(--sidebar-width);
  padding: 30px 40px;
  flex: 1;
  max-width: calc(100% - var(--sidebar-width));
  transition: all 0.3s ease;
}

/* Course content container */
.course-container {
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  box-shadow: 0 4px 20px rgba(0, 0, 0, 0.15);
  padding: 30px;
  margin-bottom: 40px;
}

/* Typography */
h1, h2, h3, h4, h5, h6 {
  margin-top: 1.5em;
  margin-bottom: 0.75em;
  font-weight: 600;
  line-height: 1.3;
  scroll-margin-top: 400px;
}

h1 {
  font-size: 2.2rem;
  color: var(--accent-blue);
  padding-bottom: 15px;
  margin-top: 10px;
  position: relative;
  display: inline-block;
}

h1:after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 100%;
  height: 3px;
  border-radius: 3px;
}

h2 {
  font-size: 1.8rem;
  color: var(--accent-blue);
  margin-top: 2em;
  position: relative;
  display: inline-block;
}

h2:after {
  content: '';
  position: absolute;
  bottom: -5px;
  left: 0;
  width: 50px;
  height: 2px;
  background: var(--accent-blue);
  border-radius: 2px;
}

h3 {
  font-size: 1.5rem;
  color: var(--accent-green);
}

h4 {
  font-size: 1.3rem;
}

p {
  margin-bottom: 1.2em;
  line-height: 1.8;
}

/* Lists */
ul, ol {
  margin-left: 0em;
  margin-bottom: 1.2em;
}

li {
  margin-bottom: 0.5em;
}

ol li {
  padding-left: 0.5em;
}


/* Code blocks */
pre, code {
  font-family: 'Monaco', 'Consolas', monospace;
  background-color: var(--bg-tertiary);
  border-radius: 4px;
}

code {
  padding: 2px 5px;
  font-size: 0.9em;
}

pre {
  padding: 15px;
  margin: 15px 0;
  overflow-x: auto;
  border: 1px solid var(--border-color);
}

pre code {
  padding: 0;
  background-color: transparent;
}

/* Equations */
.equation-block {
  background-color: var(--bg-tertiary);
  padding: 15px;
  margin: 15px 0;
  border-radius: 6px;
  border-left: 3px solid var(--accent-blue);
  overflow-x: auto;
}

.equation-inline {
  background-color: rgba(88, 166, 255, 0.1);
  padding: 2px 4px;
  border-radius: 3px;
}

/* MathJax styling */
.mjx-chtml {
  color: var(--text-primary) !important;
}

.mjx-math {
  color: var(--text-primary) !important;
}

/* Blockquotes */
blockquote {
  border-left: 4px solid var(--accent-blue);
  padding: 15px 20px;
  margin: 15px 0;
  background-color: var(--bg-tertiary);
  border-radius: 0 6px 6px 0;
  font-style: italic;
}

/* Horizontal rule */
hr {
  height: 1px;
  border: none;
  background-color: var(--border-color);
  margin: 25px 0;
}

/* Links */
a {
  color: var(--accent-blue);
  text-decoration: none;
  transition: all 0.2s ease;
}

a:hover {
  text-decoration: underline;
  color: var(--accent-purple);
}

/* Section dividers */
.section {
  margin-bottom: 40px;
  padding-bottom: 20px;
  border-bottom: 1px dashed var(--border-color);
  animation: fadeIn 0.5s ease-in-out;
  padding-top: 10px;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}

/* Course navigation */
.course-navigation {
  display: flex;
  justify-content: space-between;
  margin-top: 40px;
  padding-top: 20px;
  border-top: 1px solid var(--border-color);
}

.nav-button {
  background-color: var(--bg-tertiary);
  border: 1px solid var(--border-color);
  border-radius: 4px;
  padding: 10px 15px;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  transition: all 0.2s ease;
}

.nav-button:hover {
  background-color: var(--hover-color);
  text-decoration: none;
}

.nav-prev i {
  margin-right: 10px;
}

.nav-next i {
  margin-left: 10px;
}

/* Mobile menu toggle */
.menu-toggle {
  display: none;
  position: fixed;
  bottom: 20px;
  right: 20px;
  background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
  color: white;
  border: none;
  border-radius: 50%;
  width: 50px;
  height: 50px;
  font-size: 24px;
  cursor: pointer;
  z-index: 100;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Section Navigation Controls */
.section-navigation {
  background-color: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 8px;
  padding: 15px 20px;
  margin-bottom: 25px;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
  position: sticky;
  top: 10px;
  z-index: 10;
}

.nav-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.section-nav-btn {
  background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
  color: white;
  border: none;
  border-radius: 4px;
  padding: 10px 15px;
  font-size: 0.9rem;
  cursor: pointer;
  transition: all 0.3s ease;
  display: flex;
  align-items: center;
  gap: 8px;
}

.section-nav-btn:hover:not(:disabled) {
  transform: translateY(-2px);
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
}

.section-nav-btn:disabled {
  background: var(--bg-tertiary);
  color: var(--text-secondary);
  cursor: not-allowed;
}

.section-indicator {
  background-color: var(--bg-tertiary);
  border-radius: 20px;
  padding: 5px 15px;
  font-weight: bold;
  color: var(--accent-yellow);
}

/* Progress Bar */
.progress-bar {
  background-color: var(--bg-tertiary);
  height: 6px;
  border-radius: 3px;
  margin-top: 15px;
  overflow: hidden;
}

.progress-fill {
  background: linear-gradient(90deg, var(--accent-blue), var(--accent-purple));
  height: 100%;
  width: 0%;
  transition: width 0.4s ease-in-out;
  border-radius: 3px;
}

/* Responsive styles */
@media (max-width: 1200px) {
  :root {
    --sidebar-width: 280px;
  }
}

@media (max-width: 992px) {
  :root {
    --sidebar-width: 250px;
  }
  
  .content-area {
    padding: 20px 30px;
  }
}

@media (max-width: 768px) {
  body {
    display: block;
  }
  
  .sidebar {
    position: fixed;
    left: -300px;
    top: 120px;
    height: calc(100vh - 130px);
    z-index: 99;
    transition: left 0.3s ease;
    width: 280px;
  }
  
  .sidebar.active {
    left: 0;
  }
  
  .content-area {
    margin-left: 0;
    max-width: 100%;
  }
  
  .menu-toggle {
    display: flex;
  }
  
  .main-header {
    padding: 0 10px;
  }
  
  .logo-text {
    font-size: 1.2rem;
  }
  
  .nav-menu .nav-item:not(:first-child) {
    display: none;
  }
  
  .section-navigation {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    border-radius: 0;
    margin-bottom: 0;
    z-index: 1000;
  }
  
  .nav-controls {
    flex-wrap: wrap;
    gap: 10px;
  }
  
  .section-indicator {
    order: -1;
    width: 100%;
    text-align: center;
    margin-bottom: 10px;
  }
}

/* Print styles */
@media print {
  body {
    display: block;
    background: white;
    color: black;
  }
  
  .sidebar, .main-header, .menu-toggle, .progress-container, .section-navigation {
    display: none;
  }
  
  .content-area {
    margin-left: 0;
    max-width: 100%;
    background: white;
    color: black;
    border: none;
    box-shadow: none;
    padding: 0;
  }
  
  .course-container {
    background: white;
    border: none;
    box-shadow: none;
  }
  
  .section {
    display: block !important;
  }
}

/* Enhanced Navigation Buttons */
#nav-buttons {
  display: flex;
  justify-content: space-between;
  margin: 20px 0 30px;
  padding: 10px 0;
  border-bottom: 1px solid var(--border-color);
}

#prevBtn, #nextBtn {
  background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
  color: white;
  border: none;
  border-radius: 6px;
  padding: 12px 22px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.3s ease;
  display: flex;
  align-items: center;
  gap: 10px;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.15);
}

#prevBtn:hover, #nextBtn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 12px rgba(0, 0, 0, 0.2);
}

#prevBtn:active, #nextBtn:active {
  transform: translateY(1px);
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

#prevBtn:disabled, #nextBtn:disabled {
  background: var(--bg-tertiary);
  color: var(--text-secondary);
  cursor: not-allowed;
  transform: none;
  box-shadow: none;
}

#prevBtn::before {
  content: "←";
  font-size: 1.2rem;
}

#nextBtn::after {
  content: "→";
  font-size: 1.2rem;
}

/* Section and Subsection Animations */

/* Navigation indicators */
.navigation-indicator {
  display: flex;
  justify-content: center;
  margin: 10px 0 20px;
}

.nav-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background-color: var(--border-color);
  margin: 0 4px;
  transition: all 0.3s ease;
}

.nav-dot.active {
  background-color: var(--accent-blue);
  transform: scale(1.3);
}

/* Progress bar for navigation */
.nav-progress {
  height: 4px;
  background-color: var(--bg-tertiary);
  margin: 20px 0;
  border-radius: 2px;
  overflow: hidden;
}

.nav-progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--accent-blue), var(--accent-purple));
  transition: width 0.3s ease;
}

/* Enhanced mobile responsiveness */
@media (max-width: 768px) {
  #nav-buttons {
    position: sticky;
    bottom: 20px;
    background-color: var(--bg-secondary);
    padding: 15px;
    border-radius: 8px;
    box-shadow: 0 -4px 10px rgba(0, 0, 0, 0.2);
    z-index: 90;
    margin-top: 30px;
  }
  
  #prevBtn, #nextBtn {
    padding: 10px 15px;
    font-size: 0.9rem;
  }
}
/* Enhanced Navigation Buttons - UI changes only */
#nav-buttons {
  display: flex;
  justify-content: space-between;
  margin: 20px 0 30px;
  padding: 15px 0;
}

#prevBtn, #nextBtn {
  background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
  color: white;
  border: none;
  border-radius: 6px;
  padding: 12px 22px;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.3s ease;
  display: flex;
  align-items: center;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.15);
}

#prevBtn:hover, #nextBtn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 12px rgba(0, 0, 0, 0.2);
}

#prevBtn:active, #nextBtn:active {
  transform: translateY(1px);
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
}

#prevBtn:disabled, #nextBtn:disabled {
  background: var(--bg-tertiary);
  color: var(--text-secondary);
  cursor: not-allowed;
  transform: none;
  box-shadow: none;
}

#prevBtn::before {
  content: "←";
  font-size: 1.2rem;
  margin-right: 8px;
}

#nextBtn::after {
  content: "→";
  font-size: 1.2rem;
  margin-left: 8px;
}

/* Section and Subsection Animations - preserve existing functionality */
.section, .subsection {
  animation: fadeIn 0.5s ease-in-out;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(10px); }
  to { opacity: 1; transform: translateY(0); }
}

/* Definition and Note Boxes */
.definition-box, .note-box {
  margin: 25px 0;
  padding: 20px;
  border-radius: 8px;
  background-color: var(--bg-tertiary);
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
  border-left: 4px solid;
  position: relative;
  transition: all 0.3s ease;
}

.definition-box {
  border-left-color: var(--accent-purple);
}

.note-box {
  border-left-color: var(--accent-yellow);
}

.definition-box:hover, .note-box:hover {
  transform: translateY(-3px);
  box-shadow: 0 8px 15px rgba(0, 0, 0, 0.15);
}

.definition-box h4, .note-box h4 {
  margin-top: 0;
  display: flex;
  align-items: center;
  font-size: 1.2rem;
}

.definition-box h4::before, .note-box h4::before {
  margin-right: 10px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1rem;
  width: 28px;
  height: 28px;
}

.definition-box h4::before {
  content: "D";
  background-color: var(--accent-purple);
  color: white;
}

.note-box h4::before {
  content: "!";
  background-color: var(--accent-yellow);
  color: black;
}

/* Enhanced Table of Contents */
.toc a {
  transition: all 0.2s ease;
  border-left: 3px solid transparent;
}

.toc a:hover {
  padding-left: 15px;
}

.toc .active {
  border-left: 3px solid var(--accent-blue);
  transform: translateX(3px);
  transition: all 0.3s ease;
}

/* Code block enhancements */
pre {
  border-radius: 8px;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
  border-left: 3px solid var(--accent-blue);
}

code {
  border-radius: 4px;
}

/* Mobile enhancements */
@media (max-width: 768px) {
  #prevBtn, #nextBtn {
    padding: 10px 15px;
    font-size: 0.9rem;
  }
  
  .menu-toggle {
    background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
  }
  
  .menu-toggle:hover {
    transform: rotate(90deg);
    transition: transform 0.3s ease;
  }
}