Feat: Modify the background color of the agent canvas #3221 (#9020)

### What problem does this PR solve?

Feat: Modify the background color of the agent canvas #3221
### Type of change


- [x] New Feature (non-breaking change which adds functionality)

web/src/pages/agent/form-sheet/next.tsx

@@ -65,7 +65,7 @@ const FormSheet = ({
   return (
     <Sheet open={visible} modal={false}>
       <SheetContent
-        className={cn('top-20 p-0 flex flex-col pb-20', {
+        className={cn('top-20 p-0 flex flex-col pb-20 ', {
           'right-[620px]': chatVisible,
         })}
         closeIcon={false}