@media only screen and (min-width: 770px) {
#mi-elemento {
  position: absolute;
  display:block;
  width: 50vw;
  height: 50vh;
  top: 40px;
  left: 0;
  z-index: -1;
 /* transition: all 2s ease;*/
}

#mi-elemento.fijo {
   position: fixed;
   top: 50px; /* posicion fija */
   z-index: -1;
}
.header__section--top {
    padding-bottom: 0;
    padding-top: 0;
    display: none;
  }
  .footer__section--main {
    z-index: 9999;
    display: block;
}
  .footer__center {
    width: 100% !important;
}
.footer__center  a {
    color: #ffffff !important;
}
.footer__center    a: hover {
    color: #ffffff !important;
}