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

body {
  font-family: "Segoe UI", sans-serif;
  background-color: #f4f6fa;
  color: #222;
  line-height: 1.6;
}

header {
  background-color: #ffffff;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
  padding: 15px 40px;
}

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

.logo img {
  height: 50px;
}

.nav-links {
  list-style: none;
  display: flex;
  gap: 20px;
}

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

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

.container {
  max-width: 900px;
  margin: 40px auto;
  padding: 0 20px;
}

h1 {
  font-size: 28px;
  color: #1e3a8a;
  margin-bottom: 30px;
}

h2 {
  font-size: 22px;
  color: #1e3a8a;
  margin-bottom: 10px;
}

.exercise {
  background-color: #ffffff;
  border-left: 5px solid #1e88e5;
  padding: 20px 25px;
  margin-bottom: 25px;
  border-radius: 8px;
  box-shadow: 0 4px 10px rgba(0, 0, 0, 0.04);
}

.exercise pre {
  background-color: #f0f4fa;
  padding: 10px 15px;
  border-left: 3px solid #1e3a8a;
  font-family: monospace;
  white-space: pre-wrap;
  margin-top: 10px;
}

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