:root{
--primary: #005baa;
--nav: #003f7f;
--bg: #f4f4f9;
--card-bg: #ffffff;
--text: #333;
}


*{box-sizing:border-box}
body{
margin:0;font-family:Arial, sans-serif;background-color:var(--bg);color:var(--text);
}
header{background-color:var(--primary);color:white;padding:16px 10px;text-align:center}
nav{background-color:var(--nav);padding:10px 0;text-align:center}
nav a{color:white;text-decoration:none;margin:0 12px;font-weight:bold}
nav a:hover{text-decoration:underline}
.container{width:90%;max-width:1100px;margin:22px auto}
.intro{text-align:center;margin-bottom:18px}


/* Grid 12 ô sách */
.book-list{display:grid;gap:18px;grid-template-columns:repeat(4,1fr)}


.book{background:var(--card-bg);border:1px solid #ddd;border-radius:8px;padding:12px;text-align:center;box-shadow:0 2px 6px rgba(0,0,0,0.05)}
.book img{width:100%;height:220px;object-fit:cover;border-radius:6px}
.book h3{margin:10px 0 6px;color:var(--primary);font-size:16px}
.book p{margin:0;color:#666;font-size:14px}


footer{background:var(--primary);color:white;padding:12px 0;text-align:center;margin-top:26px}


/* Responsive: tablet 3 cột, mobile 1-2 cột */
@media (max-width:1000px){
.book-list{grid-template-columns:repeat(3,1fr)}
}
@media (max-width:700px){
.book-list{grid-template-columns:repeat(2,1fr)}
}
@media (max-width:420px){
.book-list{grid-template-columns:repeat(1,1fr)}
/* Footer chi tiết */
footer {
  background-color: var(--primary);
  color: white;
  margin-top: 40px;
  padding: 30px 0 10px;
  font-size: 14px;
}

.footer-container {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-around;
  width: 90%;
  max-width: 1100px;
  margin: 0 auto 20px;
}

.footer-section {
  flex: 1 1 250px;
  padding: 10px 20px;
}

.footer-section h3 {
  border-bottom: 2px solid #fff;
  padding-bottom: 6px;
  margin-bottom: 10px;
}

.footer-section a {
  color: #ffeb3b;
  text-decoration: none;
}

.footer-section a:hover {
  text-decoration: underline;
}

.footer-bottom {
  text-align: center;
  border-top: 1px solid rgba(255,255,255,0.3);
  margin-top: 10px;
  padding-top: 8px;
  font-size: 13px;
}

/* Responsive footer */
@media (max-width:700px) {
  .footer-container {
    flex-direction: column;
    align-items: center;
  }
  .footer-section {
    text-align: center;
  }
}

}