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

body {
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  min-height: 100vh;
  color: #333;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 20px;
}

.header {
  background: rgba(255, 255, 255, 0.95);
  border-radius: 20px;
  padding: 30px;
  margin-bottom: 30px;
  box-shadow: 0 15px 40px rgba(0, 0, 0, 0.1);
  text-align: center;
  backdrop-filter: blur(10px);
}

.header h1 {
  color: #4a5568;
  font-size: 2.5em;
  margin-bottom: 10px;
  background: linear-gradient(45deg, #667eea, #764ba2);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.section {
  background: rgba(255, 255, 255, 0.95);
  border-radius: 15px;
  margin-bottom: 25px;
  overflow: hidden;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
  backdrop-filter: blur(10px);
  transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.section:hover {
  transform: translateY(-5px);
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.15);
}

.section-header {
  background: linear-gradient(135deg, #4a5568, #2d3748);
  color: white;
  padding: 20px;
  font-size: 1.5em;
  font-weight: bold;
  cursor: pointer;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.section-header:hover {
  background: linear-gradient(135deg, #2d3748, #1a202c);
}

.section-content {
  padding: 25px;
  display: none;
}

.section-content.active {
  display: block;
  animation: slideDown 0.3s ease;
}

@keyframes slideDown {
  from {
    opacity: 0;
    transform: translateY(-10px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.toggle-icon {
  transition: transform 0.3s ease;
}

.toggle-icon.active {
  transform: rotate(180deg);
}

.code-block {
  background: #1e1e1e; /* VS dark background */
  color: #d4d4d4; /* default text */
  padding: 15px;
  border-radius: 8px;
  font-family: Consolas, "Courier New", monospace;
  overflow-x: auto;
  white-space: pre; /* keep indentation */
  border-left: 4px solid #667eea;
  box-shadow: inset 0 2px 10px rgba(0, 0, 0, 0.3);
  margin: 15px 0;
}
pre {
  border-radius: 10px;
  padding: 15px;
  overflow-x: auto;
}
.keyword {
  color: #569cd6;
} /* blue keywords */
.string {
  color: #d69d85;
} /* brownish strings */
.number {
  color: #b5cea8;
} /* green numbers */
.comment {
  color: #6a9955;
  font-style: italic;
}

.theory-box {
  background: linear-gradient(135deg, #e6fffa, #b2f5ea);
  padding: 20px;
  border-radius: 10px;
  margin: 15px 0;
  border-left: 4px solid #38b2ac;
}

.example-box {
  background: linear-gradient(135deg, #fff5f5, #fed7d7);
  padding: 20px;
  border-radius: 10px;
  margin: 15px 0;
  border-left: 4px solid #e53e3e;
}

.homework-box {
  background: linear-gradient(135deg, #f7fafc, #edf2f7);
  padding: 20px;
  border-radius: 10px;
  margin: 15px 0;
  border-left: 4px solid #4299e1;
}

.method-card {
  background: rgba(255, 255, 255, 0.8);
  border: 1px solid #e2e8f0;
  border-radius: 8px;
  padding: 15px;
  margin: 10px 0;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.05);
}

.method-name {
  font-weight: bold;
  color: #2d3748;
  font-size: 1.1em;
  margin-bottom: 8px;
}

.comparison-table {
  width: 100%;
  border-collapse: collapse;
  margin: 15px 0;
  background: white;
  border-radius: 10px;
  overflow: hidden;
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
}

.comparison-table th,
.comparison-table td {
  padding: 12px;
  text-align: left;
  border-bottom: 1px solid #e2e8f0;
}

.comparison-table th {
  background: linear-gradient(135deg, #667eea, #764ba2);
  color: white;
  font-weight: bold;
}

.comparison-table tr:hover {
  background-color: #f7fafc;
}

.task-item {
  background: rgba(255, 255, 255, 0.7);
  padding: 15px;
  border-radius: 8px;
  margin: 10px 0;
  border-left: 3px solid #4299e1;
}

ul,
ol {
  margin: 15px 0;
  padding-left: 25px;
}

li {
  margin: 8px 0;
  line-height: 1.6;
}

h2 {
  color: #2d3748;
  margin-bottom: 15px;
  font-size: 1.4em;
}

h3 {
  color: #4a5568;
  margin: 20px 0 10px 0;
  font-size: 1.2em;
}

p {
  line-height: 1.7;
  margin-bottom: 15px;
  text-align: justify;
}

.highlight {
  background: yellow;
  padding: 2px 4px;
  border-radius: 3px;
}

.warning {
  background: #fed7e2;
  border: 1px solid #f56565;
  border-radius: 8px;
  padding: 15px;
  margin: 15px 0;
}