I’m no expert on this theme. I’m just trying it out for one of my websites and had a similar problem.
Looking at your site, I noticed that there is an inline style on the div for the custom-header that has a margin-bottom of 70px. That’s what is giving you that white bar.
I found a way “around” the problem. The custom-header class has a position of relative. If you change that position to absolute, the white bar goes away.
If you are using a “child theme” then add the below CSS code to your child theme’s “style.css” file. If you are not using a child theme then you can use the following steps:
Appearance => Customize => Additional CSS
Then add this CSS code:
.custom-header {
position: absolute;
}
Make sure you add this code ABOVE or BELOW the commented lines of:
/*
You can add your own CSS here.
Click the help icon above to learn more.
*/