/* style.css - 官方正式版 (純越南語) */
* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: 'Inter', sans-serif; color: #333; line-height: 1.6; background: #fff; -webkit-font-smoothing: antialiased; }

header { display: flex; justify-content: space-between; align-items: center; padding: 20px 5%; background: white; box-shadow: 0 2px 10px rgba(0,0,0,0.1); position: sticky; top: 0; z-index: 1000; }
header .logo { display: flex; align-items: center; text-decoration: none; color: #007bff; font-weight: 800; font-size: 22px; }
header nav a { margin-left: 20px; text-decoration: none; color: #555; font-weight: 600; font-size: 15px; transition: 0.3s; }
header nav a:hover { color: #007bff; }
header nav a.btn-top { background: #007bff; color: white; padding: 8px 18px; border-radius: 50px; }

.hero { padding: 100px 5%; text-align: center; background: linear-gradient(135deg, #f8f9fa 0%, #e9ecef 100%); }
.hero h1 { font-size: 42px; font-weight: 800; margin-bottom: 20px; color: #222; }
.hero p { font-size: 18px; color: #666; margin-bottom: 30px; max-width: 700px; margin-left: auto; margin-right: auto; }

.section { padding: 80px 5%; }
.section.alt-bg { background: #f8f9fa; }
.section-title { text-align: center; font-size: 32px; font-weight: 800; margin-bottom: 50px; }

.grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); gap: 30px; }
.card { background: white; padding: 40px 30px; border-radius: 15px; box-shadow: 0 10px 30px rgba(0,0,0,0.05); text-align: center; transition: 0.3s; }
.card:hover { transform: translateY(-10px); }
.card i { font-size: 40px; color: #007bff; margin-bottom: 20px; }
.card h3 { font-size: 20px; font-weight: 700; margin-bottom: 15px; }

.item-box { background: white; margin-bottom: 15px; border-radius: 10px; overflow: hidden; border: 1px solid #eee; }
.item-header { padding: 18px 25px; cursor: pointer; display: flex; justify-content: space-between; align-items: center; font-weight: 600; transition: background 0.3s; }
.item-header:hover { background: #f0f7ff; }
.item-content { padding: 0 25px; max-height: 0; overflow: hidden; transition: 0.4s ease-out; background: #fff; color: #666; font-size: 15px; }
.item-box.active .item-content { padding: 15px 25px 25px; max-height: 1000px; border-top: 1px solid #eee; }
.item-box.active .item-header { color: #007bff; background: #f0f7ff; }

.item-content ul { list-style: none; }
.item-content li { margin-bottom: 10px; }
.item-content a { color: #007bff; text-decoration: none; }

.btn-primary { background: #007bff; color: white; padding: 15px 40px; border: none; border-radius: 50px; font-size: 16px; font-weight: 700; cursor: pointer; transition: 0.3s; display: inline-block; }
.btn-primary:hover { background: #0056b3; transform: scale(1.05); }

.registration { max-width: 500px; margin: 0 auto; background: white; padding: 40px; border-radius: 20px; box-shadow: 0 20px 40px rgba(0,0,0,0.1); }
.registration input { width: 100%; padding: 15px; margin-bottom: 15px; border: 1px solid #ddd; border-radius: 10px; }

footer { text-align: center; padding: 40px; background: #222; color: #888; font-size: 14px; }
@media (max-width: 768px) {
    .hero h1 { font-size: 32px; }
    header nav { display: none; }
}