ionic-framework/e2e/button/round/main.html

<ion-toolbar>
  <ion-title>Round Buttons</ion-title>
</ion-toolbar>

<ion-content padding>
  <button round>button</button>
  <button round light>button light</button>
  <button round secondary>button secondary</button>
  <button round danger>button danger</button>
  <button round dark>button dark</button>

  <button round outline>button</button>
  <button round light outline>button light</button>
  <button round secondary outline>button secondary</button>
  <button round danger outline>button danger</button>
  <button round dark outline>button dark</button>

</ion-content>

<style>
  button {
    display: block !important;
    margin: 8px auto !important;
  }
</style>