Sticky navigation in Impact template?

How do I apply sticky navigation bar in Impact template?

Add to Home > Design > Custom CSS

@media screen and (min-width:641px) {
/* Desktop */
header.Header.Header--top {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 999;
}
/* Remove Overlap Content */
.Site-inner {
    margin-top: 50px !important;
}}

Thank you!