* {
  box-sizing: border-box;
  font-family: Arial, sans-serif;
}

body {
  margin: 0;
  background-color: #f4f6f9;
}

header {
  background-color: #4e73df;
  color: white;
  text-align: center;
  padding: 20px;
}

main {
  max-width: 800px;
  margin: 20px auto;
}

section {
  background: white;
  padding: 20px;
  margin-bottom: 20px;
  border-radius: 10px;
  box-shadow: 0 3px 8px rgba(0,0,0,0.1);
}

h2 {
  text-align: center;
  color: #4e73df;
}

input[type="text"],
input[type="number"] {
  width: 100%;
  padding: 8px;
  margin: 5px 0 15px;
}

button {
  background-color: #4e73df;
  color: white;
  border: none;
  padding: 10px;
  cursor: pointer;
  border-radius: 5px;
  width: 100%;
}

button:hover {
  opacity: 0.9;
}

.book-item {
  border: 1px solid #ddd;
  padding: 10px;
  margin-bottom: 10px;
  border-radius: 6px;
}