header{background:linear-gradient(135deg,#2d3748,#1a202c);box-shadow:0 4px 6px rgba(0,0,0,.1);color:#fff;margin-top:0;position:sticky;top:0;width:100%;z-index:1000}.cabecera{align-items:center;display:flex;justify-content:center;margin-bottom:15px;margin-top:15px}.cabecera a{display:block;transition:transform .3s ease,opacity .3s ease}.cabecera a:hover{opacity:.9;transform:translateY(-2px)}.logo-header{height:auto;max-width:90vw;width:350px}@media (max-width:640px){.logo-header{width:280px}}