Header Issue on Landing Page with Zion Template

Site URL: https://alpaca-rhubarb-jjtf.squarespace.com/config/

Hello, I'm using the Zion template and when scrolling up and down, a black bar briefly appears in the background of the header only. Doesn't seem to be happening to any other page or area on the site while scrolling. Any help or coding would be greatly appreciated. Thank you so much as always!

Add to Design > Custom CSS

header#header {
    background-color: transparent !important;
}