/* Reset nhẹ */
* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif; color: #0f172a; }
img { max-width: 100%; display: block; }

:root{
  --bg: #000080;
  --text: #FFFFFF;
  --muted: #475569;
  --primary: #2563eb;
  --surface: #f1f5f9;
  --card: #ffffff;
  --border: #e2e8f0;
}

body { background: var(--bg); line-height: 1.6; }

.container { max-width: 980px; margin: 0 auto; padding: 0 16px; }

.site-header {
  position: sticky; top: 0; z-index: 10; background: var(--bg);
  border-bottom: 1px solid var(--border);
}
.site-header .container {
  display: flex; align-items: center; justify-content: space-between; min-height: 56px;
}
.logo { font-weight: 700; text-decoration: none; color: var(--text); font-size: 1.1rem; }
.menu-btn { display: none; border: 1px solid var(--border); background: var(--card); border-radius: 8px; padding: 6px 8px; }
.nav a { text-decoration: none; color: var(--muted); margin-left: 16px; }
.nav a:hover { color: var(--text); }

.hero {
  background: linear-gradient(180deg, #e0f2fe 0%, #ffffff 60%);
  padding: 64px 0 56px;
  text-align: center;
}
.hero h1 { margin: 0 0 8px; font-size: clamp(28px, 5vw, 40px); }
.hero p { color: var(--muted); margin: 0 0 20px; }
.btn {
  display: inline-block; background: var(--primary); color: white; text-decoration: none;
  padding: 10px 16px; border-radius: 10px; border: none; cursor: pointer; font-weight: 600;
}
.btn:hover { opacity: .9; }

.section { padding: 40px 0; }
.cards { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; }
.card {
  background: var(--card); border: 1px solid var(--border); border-radius: 14px; padding: 18px;
  box-shadow: 0 1px 0 rgba(15,23,42,0.02);
}
.card h3 { margin-top: 0; }

.contact-form { display: grid; gap: 12px; max-width: 540px; }
.contact-form label { display: grid; gap: 6px; font-weight: 600; }
.contact-form input, .contact-form textarea {
  padding: 10px 12px; border: 1px solid var(--border); border-radius: 10px; background: var(--surface);
  font: inherit;
}
.form-msg { color: var(--muted); margin: 4px 0 0; min-height: 1.2em; }

.site-footer { border-top: 1px solid var(--border); padding: 24px 0; text-align: center; color: var(--muted); }

/* Responsive */
@media (max-width: 800px){
  .cards { grid-template-columns: 1fr; }
  .menu-btn { display: inline-block; }
  .nav { display: none; position: absolute; right: 16px; top: 56px; background: var(--card); border: 1px solid var(--border);
         padding: 8px; border-radius: 12px; }
  .nav a { display: block; margin: 8px 0; }
  .nav.open { display: block; }
}