Non Responsive On Mobile

I’m using this plugin but notice that it’s not responsive on mobile devices.

When a phone is in portrait/vertical position, the message input fields stretch outside the mobile responsive theme I’m using. This causes the webpage to be pushed to the left so only 75% of the available screen space is being used by the webpage and 25% is essentially white space, except for the elongated entry fields of this plugin.

Any advice on how to correct this?

https://ww.wp.xz.cn/plugins/invite-anyone/