It’s alright. It’s just the structure we’re going for.
Now, try adding this through Appearance > Customize > Additional CSS:
.header-wrap {
position: relative !important;
}
.header-wrap > .main-navigation {
position: absolute;
bottom: 15%;
left: 50%;
z-index: 100;
width: 100%;
transform:translateX(-50%);
}
You may alter 15% to your preferred vertical position for the menu.