How to change color of edit fields?

Hey there,

I'd like to change the color of the edit fields.

Current situation:
"

Desired situation:
"

I tried several codes like:

.tnp-subscription input.tnp-email {
  background-color: #ffffff!important;
}

I put that in the custom css of the newsletter and also tried to insert it in the theme custom css field.
But nothing changes. (I know this code is only for the e-mail field, but even that doesn't change.)