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

body {
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  line-height: 1.6;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  min-height: 100vh;
  color: #333;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
  border-radius: 20px;
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.1);
  overflow: hidden;
}

.header {
  background: linear-gradient(135deg, #2c3e50, #3498db);
  color: white;
  text-align: center;
  padding: 2rem;
  position: relative;
  overflow: hidden;
}

.header::before {
  content: "";
  position: absolute;
  top: -50%;
  left: -50%;
  width: 200%;
  height: 200%;
  background: repeating-conic-gradient(
    from 0deg,
    transparent 0deg 10deg,
    rgba(255, 255, 255, 0.1) 10deg 20deg
  );
  animation: rotate 20s linear infinite;
}

.header-content {
  position: relative;
  z-index: 1;
}

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

.header h1 {
  font-size: 2.5rem;
  margin-bottom: 0.5rem;
  text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.3);
}

.duration {
  background: rgba(255, 255, 255, 0.2);
  display: inline-block;
  padding: 0.5rem 1rem;
  border-radius: 25px;
  margin-top: 1rem;
  font-weight: bold;
}

.nav-tabs {
  display: flex;
  background: #34495e;
  overflow-x: auto;
}

.nav-tab {
  flex: 1;
  padding: 1rem;
  text-align: center;
  color: white;
  cursor: pointer;
  transition: all 0.3s ease;
  border: none;
  background: none;
  font-size: 1rem;
  white-space: nowrap;
  position: relative;
}

.nav-tab:hover {
  background: rgba(52, 152, 219, 0.3);
  transform: translateY(-2px);
}

.nav-tab.active {
  background: #3498db;
  box-shadow: inset 0 -3px 0 #2980b9;
}

.content {
  padding: 2rem;
}

.tab-content {
  display: none;
  animation: fadeIn 0.5s ease;
}

.tab-content.active {
  display: block;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(20px);
  }

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

.topic-section {
  margin-bottom: 3rem;
  background: white;
  padding: 2rem;
  border-radius: 15px;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
  border-left: 5px solid #3498db;
}

.topic-section h2 {
  color: #2c3e50;
  margin-bottom: 1rem;
  font-size: 1.8rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.topic-section h3 {
  color: #34495e;
  margin: 1.5rem 0 1rem 0;
  font-size: 1.3rem;
  border-bottom: 2px solid #ecf0f1;
  padding-bottom: 0.5rem;
}

.code-block {
  background: #2c3e50;
  color: #ecf0f1;
  padding: 1.5rem;
  border-radius: 10px;
  margin: 1rem 0;
  overflow-x: auto;
  position: relative;
  border-left: 4px solid #3498db;
}

.code-block::before {
  content: "CODE";
  position: absolute;
  top: 0.5rem;
  right: 1rem;
  background: #3498db;
  color: white;
  padding: 0.2rem 0.5rem;
  border-radius: 4px;
  font-size: 0.8rem;
}

.exercise {
  background: linear-gradient(135deg, #74b9ff, #0984e3);
  color: white;
  padding: 1.5rem;
  border-radius: 15px;
  margin: 1.5rem 0;
  position: relative;
  overflow: hidden;
}

.exercise::before {
  content: "💡 EXERCISE";
  display: block;
  font-weight: bold;
  margin-bottom: 1rem;
  font-size: 1.1rem;
}

.homework {
  background: linear-gradient(135deg, #fd79a8, #e84393);
  color: white;
  padding: 1.5rem;
  border-radius: 15px;
  margin: 1.5rem 0;
  position: relative;
}

.homework::before {
  content: "📚 HOMEWORK";
  display: block;
  font-weight: bold;
  margin-bottom: 1rem;
  font-size: 1.1rem;
}

.demo-table {
  width: 100%;
  border-collapse: collapse;
  margin: 1rem 0;
  background: white;
  border-radius: 10px;
  overflow: hidden;
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
}

.demo-table th {
  background: #3498db;
  color: white;
  padding: 1rem;
  text-align: left;
}

.demo-table td {
  padding: 1rem;
  border-bottom: 1px solid #ecf0f1;
}

.demo-table tr:hover {
  background: #f8f9fa;
}

.demo-form {
  background: #f8f9fa;
  padding: 1.5rem;
  border-radius: 10px;
  margin: 1rem 0;
}

.form-group {
  margin-bottom: 1rem;
}

.form-group label {
  display: block;
  margin-bottom: 0.5rem;
  font-weight: bold;
  color: #2c3e50;
}

.form-group input,
.form-group select,
.form-group textarea {
  width: 100%;
  padding: 0.75rem;
  border: 2px solid #ecf0f1;
  border-radius: 8px;
  font-size: 1rem;
  transition: border-color 0.3s ease;
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
  outline: none;
  border-color: #3498db;
  box-shadow: 0 0 0 3px rgba(52, 152, 219, 0.1);
}

.btn {
  background: linear-gradient(135deg, #00b894, #00a085);
  color: white;
  padding: 0.75rem 1.5rem;
  border: none;
  border-radius: 25px;
  cursor: pointer;
  font-size: 1rem;
  transition: all 0.3s ease;
  box-shadow: 0 5px 15px rgba(0, 184, 148, 0.3);
}

.btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 7px 20px rgba(0, 184, 148, 0.4);
}

.timeline {
  background: #f8f9fa;
  padding: 1.5rem;
  border-radius: 15px;
  margin: 1rem 0;
}

.timeline-item {
  display: flex;
  align-items: center;
  margin-bottom: 1rem;
  padding: 1rem;
  background: white;
  border-radius: 10px;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.05);
}

.timeline-time {
  background: #3498db;
  color: white;
  padding: 0.5rem 1rem;
  border-radius: 20px;
  font-weight: bold;
  min-width: 120px;
  text-align: center;
  margin-right: 1rem;
}

.resources {
  background: linear-gradient(135deg, #a29bfe, #6c5ce7);
  color: white;
  padding: 1.5rem;
  border-radius: 15px;
  margin: 1.5rem 0;
}

.resources h3 {
  margin-bottom: 1rem;
  color: white;
}

.resources a {
  color: #ddd6fe;
  text-decoration: none;
  border-bottom: 1px solid #ddd6fe;
  transition: all 0.3s ease;
}

.resources a:hover {
  color: white;
  border-bottom-color: white;
}

.progress-bar {
  background: #ecf0f1;
  height: 6px;
  border-radius: 3px;
  margin: 1rem 0;
  overflow: hidden;
}

.progress-fill {
  background: linear-gradient(90deg, #00b894, #55a3ff);
  height: 100%;
  border-radius: 3px;
  transition: width 0.3s ease;
}

.icon {
  font-size: 1.2em;
  margin-right: 0.5rem;
}

.demo-list {
  background: #f8f9fa;
  padding: 1.5rem;
  border-radius: 10px;
  margin: 1rem 0;
}

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

.demo-list li {
  padding: 0.5rem 0;
  border-bottom: 1px solid #ecf0f1;
  position: relative;
  padding-left: 2rem;
}

.demo-list li::before {
  content: "✓";
  position: absolute;
  left: 0;
  color: #00b894;
  font-weight: bold;
}

@media (max-width: 768px) {
  .container {
    margin: 1rem;
    border-radius: 15px;
  }

  .header h1 {
    font-size: 2rem;
  }

  .nav-tabs {
    flex-direction: column;
  }

  .timeline-item {
    flex-direction: column;
    align-items: flex-start;
  }

  .timeline-time {
    margin-bottom: 0.5rem;
    margin-right: 0;
  }
}