feat(nav.scss): add styles for navigation bar

- Added styles for the navigation bar to improve the appearance and functionality of the navigation component.
- The navigation bar now has a fixed position at the bottom of the screen and is displayed as a flex container with space between and aligned center.
- The width of the navigation bar is set to 100% and the height is set using a CSS variable (--nav-height).
- Added padding to the navigation bar for spacing.
- The navigation bar has a white background and a z-index value of (--z-nav) to ensure it appears above other elements.
- The pointer-events property is set to "all" to maintain functionality while the container is locked.
- Added styles for the ".num" and ".current" classes.
- Added media queries to adjust the position and visibility of the navigation bar on smaller screens or devices without hover capability.

assets/css/_partial/_nav.scss

@@ -1,44 +0,0 @@
-@import '../_core/mixins';
-$tablet: map-get($breakpoints, 'tablet') - 1;
-
-nav {
-  display: flex;
-  justify-content: space-between;
-  align-items: center;
-
-  width: 100%;
-  height: var(--nav-height);
-  padding: 0 var(--space-standard);
-
-  position: fixed;
-  bottom: 0;
-  background: white;
-
-  z-index: var(--z-nav);
-
-  // Maintain functionality while container is locked
-  pointer-events: all;
-}
-
-.num {
-  width: 0.625em;
-  display: inline-block;
-  text-align: center;
-}
-
-.current {
-  font-style: italic;
-  text-decoration: underline;
-}
-
-@media (max-width: $tablet), (hover: none) {
-  nav {
-    top: 0;
-    position: sticky;
-  }
-
-  .index,
-  .threshold {
-    display: none;
-  }
-}