Sharepoint Online : Problem with CSS

Forms SharePoint Online
1

I'm trying to use this code to reduce the space between the line.
Few weeks ago worked fine but now no.

What I'm missing?
Thank you.

.fd-form .form-group{
  margin-bottom: 3px!important;
}
2

Dear @stefano.mazzi,
Not sure, you can try this:

.fd-form .row{
  margin-bottom: 3px!important;
}
3

Thank you, this works fine.