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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  color: #333;
  background-color: #f5f5f5;
  height: 100vh;
  overflow: hidden;
}

.app-container {
  display: flex;
  height: 100vh;
  width: 100vw;
}

/* Sidebar Styles */
.sidebar {
  width: 300px;
  background-color: #fff;
  border-right: 1px solid #ddd;
  display: flex;
  flex-direction: column;
  overflow-y: auto;
}

.sidebar h2 {
  padding: 20px;
  font-size: 1.2rem;
  border-bottom: 1px solid #eee;
  background-color: #fafafa;
}

#chapter-list {
  list-style: none;
}

.chapter-item {
  padding: 15px 20px;
  border-bottom: 1px solid #eee;
  cursor: pointer;
  transition: background-color 0.2s;
  font-size: 0.95rem;
}

.chapter-item:hover {
  background-color: #f0f0f0;
}

.chapter-item.active {
  background-color: #e6f2ff;
  border-left: 4px solid #0066cc;
  font-weight: 600;
}

/* Main Content Styles */
.main-content {
  flex: 1;
  display: flex;
  flex-direction: column;
  padding: 8px;
  gap: 10px;
  overflow-y: auto;
}

/* Content Display Area */
.content-display {
  flex: 3.5;
  background-color: #fff;
  border-radius: 8px;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.05);
  border: 1px solid #ddd;
  overflow: hidden;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 750px;
}

/* Video Player */
.video-player {
  width: 100%;
  height: 100%;
  object-fit: contain;
  background-color: #000;
}

/* Intro Text Slide */
.text-slide {
  padding: 40px;
  max-width: 800px;
  line-height: 1.6;
}

.text-slide h1 {
  font-size: 2rem;
  margin-bottom: 20px;
  color: #111;
}

.text-slide .meta {
  margin-bottom: 30px;
  padding: 20px;
  background-color: #f8f9fa;
  border-radius: 6px;
  border-left: 4px solid #333;
}

.text-slide .meta p {
  margin-bottom: 8px;
}
.text-slide .meta p:last-child {
  margin-bottom: 0;
}

.text-slide .problem {
  font-size: 1.1rem;
  margin-bottom: 20px;
}

.text-slide ul {
  margin-bottom: 30px;
  padding-left: 20px;
}

.text-slide ul li {
  margin-bottom: 10px;
  font-weight: 500;
}

.text-slide .bottom-line {
  font-weight: bold;
  padding-top: 20px;
  border-top: 1px solid #eee;
}

/* Notes Panel */
.notes-panel {
  flex: 1;
  background-color: #fff;
  border-radius: 8px;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.05);
  border: 1px solid #ddd;
  padding: 20px;
  display: flex;
  flex-direction: column;
}

.notes-panel h3 {
  margin-bottom: 15px;
  font-size: 1.1rem;
  color: #555;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  border-bottom: 1px solid #eee;
  padding-bottom: 10px;
}

#notes-content {
  line-height: 1.6;
  color: #444;
  font-size: 1.05rem;
  overflow-y: auto;
}