#principal {
  background: url('../img/fondoAgenda.png');
  /* center center fixed */
  background-repeat: no-repeat;
  background-size: cover;
}

#container-login {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background-color: rgba(255, 255, 255, 0.779);
  padding: 20px;
  border-radius: 10px;
}