body {
  font-family: Arial, sans-serif;
  background: #f0f4f8;
  margin: 0;
  padding: 0;
}

header {
  background: #4a90e2;
  color: white;
  padding: 20px;
  text-align: center;
}

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

nav a {
  color: white;
  text-decoration: none;
  font-weight: bold;
}

nav a:hover {
  text-decoration: underline;
}

main {
  padding: 20px;
  text-align: center;
}

.exercise {
  background: white;
  border: 1px solid #ddd;
  margin: 15px auto;
  padding: 20px;
  width: 60%;
  border-radius: 8px;
  box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

.site-footer {
  position: fixed;
  bottom: 0;
  width: 100%;
  text-align: center;
  padding: 10px;
  background-color: #f2f2f2;
}