responsive design pb on mobile

Hi,
I just installed the plugin on a clean new website. It’s a great one! I love it! But I have a problem on mobile size. It’s not responsive. The red color background stop in the middle, I have a white bloc coming from nowhere under the login and the input fields are not resizing to the good width, goes outside the screen. Same on my laptop when I resize the width to a phone view. Mac chrome & iphone if it matters.

https://ww.wp.xz.cn/plugins/admin-custom-login/