Dynamic Row

gistfile1.html

<!-- copiar e colar o card para testar o exemplo -->
<ion-grid style="padding-top: 60px;">
    <ion-row style="text-align: center; position: absolute;">
      <ion-card class="cardWidth">
        <ion-card-header>
          <ion-card-subtitle>Card Subtitle</ion-card-subtitle>
          <ion-card-title>Card Title</ion-card-title>
        </ion-card-header>

        <ion-card-content>
          Keep close to Nature's heart... and break clear away, once in awhile,
          and climb a mountain or spend a week in the woods. Wash your spirit clean.
        </ion-card-content>
      </ion-card>
    </ion-row>
  </ion-grid>

gistfire2.css

.cardWidth{
  width: 100%; max-width: 300px;
}