/* ===== Reset some default styles ===== */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: 'Helvetica Neue', Arial, sans-serif;
  line-height: 1.6;
  background-color: #f9f9f9;
  color: #333;
  padding: 0 1rem;
}

a {
  text-decoration: none;
  color: #1a73e8;
}

a:hover {
  text-decoration: underline;
}

/* ===== Header ===== */
header {
  text-align: center;
  padding: 2rem 0;
  background-color: #fff;
  border-bottom: 1px solid #ddd;
}

header h1 {
  font-size: 2.5rem;
  margin-bottom: 0.5rem;
}

header p {
  font-size: 1.1rem;
  color: #555;
}

/* ===== Main content ===== */
main {
  max-width: 900px;
  margin: 2rem auto;
}

h2 {
  font-size: 2rem;
  margin-bottom: 1rem;
  color: #222;
}

/* ===== Book list ===== */
ul {
  list-style-type: none;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 1rem;
}

ul li {
  background-color: #fff;
  padding: 1rem;
  border-radius: 8px;
  box-shadow: 0 2px 6px rgba(0,0,0,0.05);
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

ul li:hover {
  transform: translateY(-3px);
  box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

ul li a {
  font-weight: bold;
  display: block;
  margin-bottom: 0.5rem;
}

ul li a::after {
  content: '';
  display: inline-block;
}

/* ===== Sections ===== */
section {
  margin-bottom: 2rem;
}

section p {
  font-size: 0.95rem;
  color: #666;
}

/* ===== Footer ===== */
footer {
  text-align: center;
  padding: 1.5rem 0;
  background-color: #fff;
  border-top: 1px solid #ddd;
  font-size: 0.9rem;
  color: #555;
}

/* ===== Responsive ===== */
@media (max-width: 600px) {
  header h1 {
    font-size: 2rem;
  }

  h2 {
    font-size: 1.5rem;
  }
  
  ul {
    grid-template-columns: 1fr;
  }
}

.isbn-tag {
  display: inline-block;
  margin-top: 6px;
  margin-left: 8px;

  padding: 4px 10px;
  font-size: 0.75rem;
  font-weight: 500;
  line-height: 1;

  color: #555;
  background-color: #f2f3f5;

  border-radius: 999px; /* pill shape */
  border: 1px solid #e0e0e0;

  white-space: nowrap;
}
.book-list li {
  margin-bottom: 14px;
}
.isbn-tag:hover {
  background-color: #e8e9ec;
  color: #333;
}