如何使用Angular5材质替换datePicker中的图标？

npm install --save @angular/material @angular/cdk

import { MatDatepickerModule, MatIconModule } from '@angular/material';

@NgModule({
  imports: [
    // ...
    MatDatepickerModule,
    MatIconModule
  ],
  // ...
})
export class AppModule { }

<mat-form-field>
  <input matInput [matDatepicker]="picker" placeholder="选择日期">
  <mat-datepicker-toggle matSuffix [for]="picker"></mat-datepicker-toggle>
  <mat-datepicker #picker></mat-datepicker>
</mat-form-field>

<mat-form-field>
  <input matInput [matDatepicker]="picker" placeholder="选择日期">
  <mat-icon matDatepickerToggleIcon>event</mat-icon>
  <mat-datepicker #picker></mat-datepicker>
</mat-form-field>