* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: Arial, sans-serif;
}
body {
  background-color: #f3f4f6;
  color: #333;
  scroll-behavior: smooth;
}
.dau {
  width: 100%;
  height: 250px;
  position: relative;
  overflow: hidden;
}
.dau .slide {
  position: absolute;
  width: 100%;
  height: 100%;
  background-size: cover;
  background-position: center;
  opacity: 0;
  animation: slideshow 9s infinite;
}
.dau .slide:nth-child(1) {
  animation-delay: 0s;
}
.dau .slide:nth-child(2) {
  animation-delay: 3s;
}
.dau .slide:nth-child(3) {
  animation-delay: 6s;
}
@keyframes slideshow {
  0% { opacity: 0; }
  10% { opacity: 1; }
  30% { opacity: 1; }
  40% { opacity: 0; }
  100% { opacity: 0; }
}
.menu {
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: #0ea5a3;
  padding: 12px 0;
  gap: 50px;
}
.menu a {
  color: white;
  text-decoration: none;
  font-size: 18px;
  font-weight: bold;
  transition: 0.3s;
}
.menu a:hover {
  color: #facc15;
}
.gioithieu {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  padding: 40px 80px;
  gap: 40px;
}
.video {
  flex: 1;
}
.noidung {
  flex: 1;
  font-size: 16px;
  color: #475569;
}
.tieude {
  font-size: 24px;
  font-weight: bold;
  color: #0ea5a3;
  margin: 40px 0 20px 80px;
  text-align: left;
}
.khungsach {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 24px;
  padding: 0 80px;
}
.sach {
  background-color: white;
  border-radius: 10px;
  overflow: hidden;
  box-shadow: 0 4px 12px rgba(0,0,0,0.1);
  transition: transform 0.2s, box-shadow 0.2s;
}
.sach:hover {
  transform: translateY(-6px);
  box-shadow: 0 6px 20px rgba(0,0,0,0.15);
}
.sach img {
  width: 100%;
  height: 300px;
  object-fit: contain;
  background-color: #f9fafb;
  padding: 10px;
  border-bottom: 1px solid #e5e7eb;
}
.noidungsach {
  padding: 12px;
}
.tensach {
  font-size: 16px;
  font-weight: bold;
  color: #0f172a;
  margin-bottom: 6px;
}
.tacgia {
  font-size: 14px;
  color: #475569;
  margin-bottom: 4px;
}
.sotrang {
  font-size: 13px;
  color: #64748b;
}
.chan {
  background-color: #0033A0;
  color: white;
  text-align: center;
  padding: 40px 20px;
  line-height: 1.8;
}
.chan h2 {
  font-size: 24px;
  margin-bottom: 10px;
  color: white;
}
.logo {
  width: 80px;
  height: auto;
  margin: 10px 0 20px 0;
}
.chan p {
  margin: 6px 0;
  font-size: 16px;
}
@media (max-width: 768px) {
  .gioithieu {
    flex-direction: column;
    padding: 20px;
  }
  .khungsach {
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    padding: 0 20px;
  }
  .tieude {
    margin-left: 20px;
  }
}