css
/* Reset muy simple */
* { box-sizing: border-box; }
body {
  font-family: system-ui, Arial, sans-serif;
  margin: 0;
  background: #f4f7fb;
  color: #111;
  line-height: 1.4;
}

/* Header */
.site-header {
  background: linear-gradient(90deg,#003f7f,#005fbf);
  color: #fff;
  padding: 1rem;
  position: sticky;
  top: 0;
  z-index: 100;
}

/* Título y botón de menú móvil */
.site-header h1 { margin: 0; font-size: 1.25rem; display: inline-block; }
.nav-toggle {
  display: none; /* sólo visible en móvil */
  margin-left: 1rem;
  background: transparent;
  color: #fff;
  border: 1px solid rgba(255,255,255,0.2);
  padding: 6px 10px;
  border-radius: 6px;
}

/* Menú principal */
.main-nav ul {
  list-style: none;
  margin: 0.6rem 0 0 0;
  padding: 0;
  display: flex;
  gap: 0.25rem;
  align-items: center;
}

.main-nav a, .main-nav button {
  text-decoration: none;
  color: #fff;
  padding: 8px 12px;
  display: inline-block;
  background: rgba(255,255,255,0.06);
  border-radius: 6px;
  border: none;
  cursor: pointer;
  font: inherit;
}

/* Submenu */
.has-submenu { position: relative; }
.submenu {
  position: absolute;
  left: 0;
  top: calc(100% + 6px);
  min-width: 170px;
  display: none;
  background: #0066aa;
  border-radius: 6px;
  padding: 6px 0;
  box-shadow: 0 6px 14px rgba(0,0,0,0.15);
}
.submenu li { display: block; }
.submenu a {
  display: block;
  padding: 8px 12px;
  color: #fff;
}
.submenu a:hover { background: rgba(0,0,0,0.08); }

/* Mostrar por hover en desktop */
@media (hover: hover) {
  .has-submenu:hover > .submenu { display: block; }
}

/* Estilos del contenido */
.section {
  max-width: 900px;
  margin: 24px auto;
  background: #fff;
  padding: 16px;
  border-radius: 8px;
  box-shadow: 0 2px 6px rgba(0,0,0,0.06);
}

/* Tabla de ejemplo */
.demo-table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 12px;
}
.demo-table caption { caption-side: top; font-weight: bold; margin-bottom: 6px; }
.demo-table th, .demo-table td {
  border: 1px solid #ddd;
  padding: 10px;
  text-align: center;
}
.demo-table thead th {
  background: #005fbf;
  color: white;
}

/* Footer */
.site-footer {
  text-align: center;
  padding: 12px;
  margin-top: 24px;
  background: #003f7f;
  color: white;
}

/* Responsive: menú en columnas para móvil */
@media (max-width: 720px) {
  .nav-toggle { display: inline-block; }

  .main-nav {
    display: none;
  }

  .main-nav[aria-hidden="false"] {
    display: block;
    background: #005fbf;
    margin-top: 10px;
    border-radius: 8px;
    padding: 8px;
  }

  .main-nav ul {
    flex-direction: column;
    gap: 6px;
  }

  .submenu {
    position: static;
    display: none;
    margin-left: 8px;
    background: transparent;
    box-shadow: none;
    padding-left: 0;
  }

  .submenu[aria-hidden="false"] { display: block; }
}