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

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

extensions/cornerstone/src/components/WindowLevelActionMenu/VolumeRenderingPresetsContent.tsx

@@ -61,7 +61,7 @@ export function VolumeRenderingPresetsContent({ presets, viewportId, hide }: Pro
                 className={
                   selectedPreset?.name === preset.name
                     ? 'border-highlight h-[75px] w-[95px] max-w-none rounded border-2'
-                    : 'hover:border-highlight h-[75px] w-[95px] max-w-none rounded border-2 border-black'
+                    : 'hover:border-highlight h-[75px] w-[95px] max-w-none rounded border-2 border-background'
                 }
               />
               <label className="text-muted-foreground mt-1 text-left text-xs">