The vertical position will be wrong if you use this theme along with Welcome Banner theme component even if the banner is hidden.
See:
https://meta.discourse.org/t/welcome-link-banner/218743/61?u=canapin
The most straightforward way to circumvent the issue is adding this CSS to your theme:
.above-main-container-outlet.welcome-link-banner-connectors {
margin-bottom: 0;
}