body {
  font-family: 'Poppins', sans-serif;
  background: linear-gradient(160deg, #f0f0f5, #e6e5ea);
  margin: 0;
  padding: 0;
  color: #2c2c2c;
}
header {
  background: #4e73df;
  color: white;
  padding: 10px;
  text-align: center;
}
.btn-nav {
  background: white;
  border: none;
  color: #4e73df;
  padding: 8px 12px;
  margin: 4px;
  border-radius: 6px;
  cursor: pointer;
  transition: 0.3s;
}
.btn-nav:hover { background: #dfe6ff; }
.pantalla { display: none; text-align: center; margin-top: 20px; }
.pantalla.activa { display: block; }
input, button { padding: 8px; margin: 5px; border-radius: 4px; border: 1px solid #aaa; }
table { width: 90%; margin: 10px auto; border-collapse: collapse; }
th, td { padding: 8px; border: 1px solid #999; }
.pie-pagina {
  background: #4e73df; color: white; padding: 10px; text-align: center;
  position: fixed; bottom: 0; width: 100%;
}
.error { color: red; }