Fix element overlap for nav module

[devdanio]

Root nav elements with drop downs prevent the next siblings root nav element from being clickable. That is because the drop down elements are rendered on top of the root nav element, despite not being visible on screen. Here's what it looks like when there is no overflow:hidden. I can only click on "Blog" by hovering over the "Bl", otherwise, I would be clicking on the hidden drop down nav menu.

[netlify[bot]]

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🔨 Latest commit	0f1b9e2b3f4b19ad65d9f3d0015b2bf1bc677719