Custom CSS does not apply on the /register page

[Himura2la]

I want to hide some fields from the registration form using the following CSS

form[action="/register"] > div:has(#indirizzo),
form[action="/register"] > div:has(#telefono),
form[action="/register"] > div > div:has(#data_nascita),
form[action="/register"] > div:has(#cod_fiscale) {
  display: none
}

but the "Custom CSS" feature in /admin/settings?tab=advanced#advanced does not insert the specified CSS onto the /register page

TBH, I don't see the "Custom CSS" feature working at all

[Himura2la]

Same for Custom CSS in a theme /admin/themes/9/customize