Previous commit was removing margin-left: 0

style. This revert back this change and add more
consistencies with the `navStore` and classes.

src/UIShell/Content.svelte

@@ -1,8 +1,24 @@
 <script>
   /** Specify the id for the main element */
   export let id = "main-content";
+
+  import { isSideNavExpanded, isSideNavRail } from "./navStore";
+
+  /**
+   * By default, the `SideNav` applies a left margin of `3rem` to `Content`
+   * if it's a sibling component (e.g., .bx--side-nav ~ .bx--content).
+   *
+   * We manually unset the left margin if the `SideNav`
+   * is collapsed and if it's not the `rail` variant.
+   */
+  $: unsetLeftMargin = !$isSideNavRail && !$isSideNavExpanded;
 </script>
 
-<main id="{id}" class:bx--content="{true}" {...$$restProps}>
+<main
+  id="{id}"
+  class:bx--content="{true}"
+  style="{unsetLeftMargin ? 'margin-left: 0' : ''}"
+  {...$$restProps}
+>
   <slot />
 </main>