docs: Tweak TOC rootMargin parameter

To take into account the top header.

src/routes/docs/_TableOfContents.svelte

@@ -4,6 +4,7 @@
   import TocItems, { type TocItem } from "./_TocItems.svelte";
 
   export let el: HTMLElement | null;
+  export let rootMargin = "0% 0% -80% 0%";
 
   let runWithCleanup = createRunWithCleanup();
   let activeId: string | undefined;
@@ -55,7 +56,7 @@
           }
         });
       },
-      { rootMargin: `0% 0% -80% 0%` }
+      { rootMargin }
     );
   });
 

src/routes/docs/__layout.svelte

@@ -28,7 +28,7 @@
       class="sticky top-0 pt-20 pb-4 -mt-[61px] max-h-screen overflow-y-auto"
     >
       {#key $page}
-        <TableOfContents {el} />
+        <TableOfContents {el} rootMargin="-61px 0% -85% 0%" />
       {/key}
     </nav>
   </div>