Issue with FormControl

Hi,
I’m new to Ionic 4 and I habe a stupid issue.
I create a page and wants to build a form. The page doesn’t render correctly.
The area with the form is very small and there is a scollbar.

What is my mistake?

<ion-content>

  <form>
   <ion-item>
      <ion-label>Firstname</ion-label>
      <ion-input type="text" formControlName="firstName"></ion-input>
    </ion-item>
    <ion-item>
        <ion-label>Lastname</ion-label>
        <ion-input type="text" formControlName="lastName"></ion-input>
    </ion-item>
</form>

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