Want to set framework part styles, get error

Ionic Framework Ionic Vue
#1

according to this

I should be able to set some of the shadow dom elements styles like this

ion-content::part(scroll)
    height:91%;

but when I put that in my component section I get this error

(33:13) Double colon

  31 | }
  32 | 
> 33 | ion-content::part(scroll)
     |             ^
  34 |     height:91%;
  35 | }

am I supposed to put this someplace else?

#2

The syntax in the styles block is

::part(scroll){
}