Ionic 3 not applying default style to button

I've started a blank project with Ionic 3 and the default style is not applying to the buttons.

I'm using a default button with

<button ion-button>Prueba</button>

But I get this

Am I missing something?

UPDATE

Using

<ion-button block color="primary">Acceder</ion-button>

Fix the problem but I notice that is not using full width in the div than contains the button

<div padding>
   <ion-button block color="primary">Acceder</ion-button>
</div>

Not sure where is the problem