button not responsive

So i’m using an Avada theme and I inserted a button that opens Login-with-Ajax plugin (Button name: Acceder / Registrarse).

The website is siodental

I inserted the code in the Header #4 Banner custom code in Avada theme options.

The thing is, the button is hidden when the width of the page is low and therefore it isn’t responsive.

Any ideas?

Thank you.