Ionic 4 Expandable Accordion

Ok what I can see is that other people are using ion-button with ion-item attribute but I can see there’s no ion-item css/styling applied:

<ion-button ion-item></ion-button> 

Same thing happens if I use ion-item and apply a ion-button / button attribute, no css rule is applied, meaning that my application might be missing css files or something though I cannot figure out what files those are. Any clue anyone?