Modifying input field size

I am trying to modify the size of specific input fields, not the whoole form. On the same line, I would like to have a small drop down field. followed by a text area field.

In order to achieve the first part (the small field), I gave it the “short” ID and added the followiing custom CSS to the page, but it does not work.

#short {
width: 200px;
}

Here is the link to the page:

http://www.composites-aragon.es/wp/contacto/oportunidades/

The field I am trying to mofy is the third one, that read “Documento”

https://ww.wp.xz.cn/plugins/contact-form-7/