In each item customize settings section, scroll down you will see a subsection called “Item Layout”, in this subsection you can customize item margin, align and merge items.
Set your item margin.
Set your item content align.
If your item have a lot of space and you don’t known the with of this item because the with is dynamic, to remove empty that empty space maybe you will need merge this item with left or right items. See the example below:
In the image above, you can see Log & Site identity and Primary Item fill all slots of Header Main row (1), and frontend display (2), we can see have a lot of space (3), to remove that empty space we’ll need merge Logo with Primary Menu item. See example after merged – the empty space removed.