Is there some configuration to display the Navbar's itens as Justified: Fill?
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Well based on your screen shot, select the Nav component under the Navbar Collapse component in the Overview pane (bottom/left). Then in the Options pane (top/right) select the Gear Cog icon scroll down and expand the Flexbox section. For the Grow option set that to Yes then for the Justify Content set that to Around. Probably gets you what you want. You do need the grow so the UL element expands the width of the navbar section, but you can just specify width to the LI elements if you want more control over their widths. That can also be in conjunction with the Justify Content as well.