Form not responsive on smartphone

I cant make my webpage look responsive when looking in smartphone. is a google sites, where i have try iframe and javascript, but i looks, despite many changes, not ok when looking at the smartphone.

what can i do?

https://soporte.ifra-asesores.com/empresas/formularios/registrodeclaraciondemanda

Hi,

We apologize for the inconvenience.

Can you send us a screenshot of how it looks like on your smartphone? I checked the website and it looks fine on my mobile device.

Here's a guide on how to post a screenshot on our forum. 

How-to-Post-Screenshots-to-Our-Support-Forum

Looking forward to your response.