fix: Fix Backlinks not applying the display class (#519)

* fix: Fix `Backlinks` not applying the display class

Fix #518

* fix: Apply `displayClass` to all layout components

* refactor: Use same style

* fix: Remove `undefined` class using coalescing operator

quartz/components/Explorer.tsx

@@ -86,7 +86,7 @@ export default ((userOpts?: Partial<Options>) => {
   function Explorer({ allFiles, displayClass, fileData }: QuartzComponentProps) {
     constructFileTree(allFiles)
     return (
-      <div class={`explorer ${displayClass}`}>
+      <div class={`explorer ${displayClass ?? ""}`}>
         <button
           type="button"
           id="explorer"