How to modify the width only on a specific field?

I would like to modify the width only on a specific field from the configurable list. How i can do it?

We can try it using the custom CSS code. Can you please let us know the form URL of your form and a screenshot of the field you want to adjust?

Guide: 

- https://www.jotform.com/help/401-Where-to-Find-My-Form-URL

- https://www.jotform.com/help/438-How-to-Post-Screenshots-to-Our-Support-Forum