这个脚本是如何工作的，为什么用户不能选择开发人员工具中的消息框来删除它

Go to https://app.sequoiahack.com/ in chrome browser. Don't put you email id and just click "Get started". It will prompt you to fill out email field,don't do it just close the tab. Now the message box is still there (stucked). I tried to delete it using chrome developers tools but can't select it to remove it from html code. I am interested in knowing how can a developer create such a box and whats the cleaning activity/code required to remove it which developer has forgotten to add in the application/web page code. Please see attached screenshot. in chrome br