@media screen and (max-width: 979px) {
  .off-canvas #off-canvas-nav {
    position: fixed;
    top: 0;
    bottom: 0;
  }
  .off-canvas #off-canvas-nav .t3-mainnav {
    top: 0 !important;
    bottom: 0 !important;
    overflow-y: scroll;
  }
}