Here is a code that should be added to the Custom CSS field. We have added it already

.site-logo {
      overflow: hidden;
}

.basel-logo-wrap {
    position: relative;
      transition: all .2s ease;
}

.basel-logo {
      height: 105px;
      display: block;
}

.basel-logo:hover {
      text-decoration: none;
}

.basel-logo:before {
    content: "";
      position: relative;
      display: inline-block;
      height: 100%;
     vertical-align: middle;
}

.basel-second-logo {
    position: absolute;
     left: 0;
      right: 0;
      top: 100%;
      opacity: 0;
      visibility: hidden:
}

.act-scroll .basel-logo-wrap {
    transform: translateY(-75px);
    -webkit-transform: translateY(-75px);
}

.act-scroll .basel-second-logo {
    opacity: 1;
      visibility: visible;
}

.act-scroll .basel-logo {
    height: 75px;
}

Regards