Hello @ConjuringMind,
Thanks for writing to us.
I would suggest you add the background color on the Header bar and set it as sticky.

Now uncheck the Hide initially settings. Add this custom CSS code on the customize -->Element CSS.
Add this style there.
$el.x-bar.x-bar-fixed {
background-color: rgb(141 231 0 / 50%);
}
Please feel free to change the color code as per your design. The purpose of providing custom CSS is to show you how to add CSS code to your site. Writing custom CSS is outside the scope of our theme support. If you need more customization, you need to learn CSS and learn how to use the browser’s element inspector or you can subscribe to One where customization questions are answered.
Hope it helps.
Thanks