feat(ui): style copy button on ToastWithSessionRefDescription

Author: psychedelicious

invokeai/frontend/web/src/features/toast/ToastWithSessionRefDescription.tsx

@@ -20,8 +20,11 @@ export default function ToastWithSessionRefDescription({ message, sessionId }: P
           icon={<PiCopyBold />}
           onClick={onCopy.bind(null, sessionId)}
           variant="ghost"
+          sx={sx}
         />
       </Flex>
     </Flex>
   );
 }
+
+const sx = { svg: { fill: 'base.50' } };