无法单击垫步进标头

Question

我有一个简单的mat-stepper代码

<mat-horizontal-stepper [linear]="isLinear" #stepper>
<mat-step [stepControl]="firstFormGroup">
  <form [formGroup]="firstFormGroup">
    <ng-template matStepLabel>Fill out your name</ng-template>
    <mat-form-field>
      <input matInput placeholder="Last name, First name" formControlName="firstCtrl" required>
    </mat-form-field>
    <div>
      <button mat-button matStepperNext>Next</button>
    </div>
  </form>
</mat-step>
<mat-step [stepControl]="secondFormGroup">
  <form [formGroup]="secondFormGroup">
    <ng-template matStepLabel>Fill out your address</ng-template>
    <mat-form-field>
      <input matInput placeholder="Address" formControlName="secondCtrl" required>
    </mat-form-field>
    <div>
      <button mat-button matStepperPrevious>Back</button>
      <button mat-button matStepperNext>Next</button>
    </div>
  </form>
</mat-step>
<mat-step>
  <ng-template matStepLabel>Done</ng-template>
  You are now done.
  <div>
    <button mat-button matStepperPrevious>Back</button>
    <button mat-button (click)="stepper.reset()">Reset</button>
  </div>
</mat-step>

我无法单击步进标题。我该怎么办？