body {
  margin: 0;
  font-family: "Segoe UI", sans-serif;
  background-color: #f4f6fa;
  color: #222;
}

header {
  background-color: #ffffff;
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 15px 40px;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.logo img {
  height: 50px;
}

nav ul {
  display: flex;
  gap: 20px;
  list-style: none;
  padding: 0;
  margin: 0;
}

nav ul li a {
  text-decoration: none;
  color: #1e3a8a;
  font-weight: 500;
  transition: 0.3s;
}

nav ul li a:hover,
nav ul li a.active {
  color: #1e88e5;
}

.learning-layout {
  display: flex;
  padding: 40px;
  gap: 40px;
}

.chapter-list {
  width: 250px;
  background-color: #fff;
  padding: 20px;
  border-radius: 12px;
  box-shadow: 0 5px 10px rgba(0, 0, 0, 0.05);
}

.chapter-list h3 {
  color: #1e3a8a;
  margin-bottom: 15px;
}

.chapter-list ul {
  list-style: none;
  padding: 0;
  margin: 0;
}

.chapter-list li {
  padding: 12px 16px;
  border-radius: 8px;
  margin-bottom: 10px;
  background-color: #f0f4fb;
  cursor: pointer;
  transition: background-color 0.3s;
}

.chapter-list li:hover {
  background-color: #dbeafe;
}

.chapter-list li.active {
  background-color: #1e3a8a;
  color: white;
  font-weight: bold;
}

.chapter-content {
  flex: 1;
}

.chapter-content h2 {
  color: #1e3a8a;
  font-size: 24px;
  margin-bottom: 25px;
}

.lesson-cards {
  display: flex;
  gap: 30px;
  flex-wrap: wrap;
}

.lesson-card {
  background-color: white;
  padding: 25px;
  border-radius: 12px;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.06);
  flex: 1 1 300px;
}

.lesson-card h4 {
  color: #1e3a8a;
  margin-bottom: 10px;
}

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

.btn {
  background-color: #1e88e5;
  color: white;
  padding: 10px 18px;
  border: none;
  border-radius: 6px;
  text-decoration: none;
  font-weight: bold;
  display: inline-block;
}

.btn:hover {
  background-color: #1669c1;
}

footer {
  text-align: center;
  padding: 20px;
  background-color: #1e3a8a;
  color: white;
  margin-top: 40px;
}