fix(colors): Replace hardcoded black with background color token (#5815)

* Update all black to background

* remove --canvas token, keep intentional bg-black

* Move bg-black from grid container to individual viewport panes

---------

Co-authored-by: Alireza <ar.sedghi@gmail.com>

platform/ui-next/src/components/Thumbnail/Thumbnail.tsx

@@ -67,7 +67,7 @@ const Thumbnail = ({
         )}
       >
         <div className="h-[114px] w-[128px]">
-          <div className="relative bg-black">
+          <div className="relative bg-background">
             {imageSrc ? (
               <img
                 src={imageSrc}