home.page.html

<ion-header>
 <ion-toolbar>
   <ion-buttons slot="secondary">
     <ion-button fill="outline">
       <ion-icon slot="start" name="star"></ion-icon>
       Star
     </ion-button>
   </ion-buttons>
   <ion-title>Theme Demo</ion-title>
   <ion-buttons slot="primary">
     <ion-button color="danger" fill="outline">
       Edit
       <ion-icon slot="end" name="create"></ion-icon>
     </ion-button>
   </ion-buttons>
 </ion-toolbar>
</ion-header>

<ion-content>
 <ion-button (click)="colorIt()">Color Theme</ion-button>
 <ion-button (click)="setTheme('dark')">Dark Theme</ion-button>
 <ion-button (click)="setTheme('light')">Light Theme</ion-button>
</ion-content>