Remove White Space

What white space are you referring to exactly…between the menu and the main content?

Ah, the screenshot helped. You need some custom CSS to change that in both areas, so in your customizer’s Additional CSS tab, paste this:

For the header and branding area:

@media screen and (min-width: 30em) {
.site-branding {
    padding: 1em 0;
}
}

You can adjust the padding to your preference. The theme’s padding is 3em, but I did it as 1em.

For the content area, this might be a bit trickier, but the theme scripts adds a dynamic top margin to it, so we have to force a new margin with:

.site-content .wrap {
    margin-top: 40px!important;
}

I did 40px, but you can do whatever you prefer.

For the branding, make sure you have the exact code as I have below pasted into the Additional CSS tab of the customizer:

@media screen and (min-width: 30em) {
.site-branding {
    padding: 1em 0;
}
}

For the other part, I forgot about the “padding”, so also add this:

@media screen and (min-width: 48em) {
.site-content {
    padding: 5.5em 0 0;
}
}
.site-content {
    padding: 2.5em 0 0;
}

The padding values you see as 5.5em and also 2.5em should be changed to your preference. So try changing 5.5em to something like 2em and change the 2.5em one to like 1em