Line instead of e-mail box in Newsletter Form, when error occurs

Hi there,

I'm reaching out because I'm encountering an issue with the CSS code for my newsletter form. I customized the form style, specifically by replacing the email address box with a simple line. The problem arises whenever an error occurs in the form submission ('email address is required'): the line disappears, and the box reverts to its default appearance. I would like the line to remain visible even when an error occurs, maintaining the consistent design of the form.

Can anyone help me solve this issue?

Thank you!