go to demo.neontheme.com/ open the chat from the top then open any chat tab from the right after that go to anotepad.com/notes/gfheqtek and copy the all payloads and paste it in the chat then send it ,as you can see the xss worked if you close the chat and open it it's will work again so it's stored xss after
note:
it's workes on firefox without user interaction but it's need user interaction on chrome browser