Why view is re-render every time that click on control


I have some problem with view is re-render when click the buttons that I code to change FontSize. (3 buttons )
the iframe that I put YouTube player reload and stop playing.


Please show the code for these buttons and the functionality behind it.

  <button ion-button icon-only color="light" outline (click)="changeFontSize(0.2)">
         <img src="assets/btn_fontsize_l.png" style="max-height:100%;">
    changeFontSize(fontsize) {
        this.fontsizeTitle = (1 + fontsize) + "em";
        this.fontsize = (0.8 + fontsize) + "em";
 <ion-col col-12>
     <pre class="news-details thsarabun" [innerHTML]="item.newsDetail" style="color:#ffffff;word-wrap: break-word!important;white-space: initial;" [ngStyle]="{'font-size': fontsize}"></pre>

code just change style of element but view is look like re-render all that make mt iframe that playing video has stop.