Hi Willya,
Here’s a CSS you may try adding through Appearance > Customize > Additional CSS:
@media (min-width: 1025px) {
div#primary-menu {
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%,-50%);
}
header#masthead .inside-header {
position: relative;
}
nav#site-navigation, nav#site-navigation .inside-navigation.grid-container {
position: static;
}
}
Take note though that at some point, at around 1040px, the menu wraps because it doesn’t fit the available space anymore. You could either add another CSS to make the menu font size smaller, or make this code only work up to 1040px.
Hope this helps!