Bug: Navbar mode icon is partially hidden on widths between 767px and 799px

**This is a Bug Report**

**Problem:**
On screen widths between 767px and 799px, the main navbar items take up too much horizontal space. This pushes the dark/light mode toggle icon off the edge of the screen, causing it to be partially hidden/clipped.

**Proposed Solution:**
Reduce the horizontal margin (`padding`/`margin`) between the navbar items on smaller screens so everything fits within the viewport.

Specifically, in `layouts/partials/navbar.html`, change the margin class on the main menu items (`