feat(preview-server): darken canvas when dark mode is enabled (#2652)

Author: gabrielmfern

.changeset/many-spoons-design.md

@@ -0,0 +1,5 @@
+---
+"@react-email/preview-server": patch
+---
+
+darken the canvas background when dark mode is enabled

packages/preview-server/src/app/preview/[...slug]/preview.tsx

@@ -138,6 +138,7 @@ const Preview = ({ emailTitle, className, ...props }: PreviewProps) => {
         className={cn(
           'h-[calc(100%-3.5rem-2.375rem)] will-change-[height] flex p-4 transition-[height] duration-300 relative',
           activeView === 'preview' && 'bg-gray-200',
+          activeView === 'preview' && isDarkModeEnabled && 'bg-gray-400',
           toolbarToggled && 'h-[calc(100%-3.5rem-13rem)]',
           className,
         )}