Add icon button style.

frontend/src/app/components/header/header.component.html

@@ -1,6 +1,7 @@
 <div class="left">
     <button type="button"
             (click)="sideMenu.open()"
+            class="cod-btn icon"
             matTooltip="Click to show side menu" 
             matRipple 
             i18n-matTooltip>
@@ -18,8 +19,8 @@
 
 <div class="right">
     @if (isAuthenticated) {
-        <button mat-button
-                class="button"
+        <button type="button"
+                class="cod-btn icon"
                 [matMenuTriggerFor]="authenticatedUserMenu" 
                 matRipple>
             <mat-icon>more_vert</mat-icon>