Question: The default icon for toggling a `mat-expansion-panel` is `>`. Setting `hideToggle` true just hides the toggle icon. Is there any way to change it? I found nothing in the official documentation. I want to use `+` or `-` icon if the state is closed or opened respectively.

Answer: 
There is a class `.mat-expanded` which is applied to a `<mat-expansion-panel>`

So you can just **use CSS to change the icon**, no JS required.

* To change arrow down to up:

```css
.mat-expanded .mat-expansion-panel-header-title .material-icons{
  transform: rotate(180deg);
}

```

```
    <mat-panel-title>
      <span class="material-icons">expand_more</span>
      Panel with icon `transform`
    </mat-panel-title>

```

* To swap icons:

```css
.mat-expansion-panel-header-title .open,
.mat-expanded .mat-expansion-panel-header-title .close{
  display: inline-block;
}
.mat-expanded .mat-expansion-panel-header-title .open,
.mat-expansion-panel-header-title .close{
  display: none;
}

```

```
    <mat-panel-title>
      <span class="material-icons open">open_in_full</span>
      <span class="material-icons close">close_fullscreen</span>
      Panel with open/close
    </mat-panel-title>

```

Here is a link to a demo [https://stackblitz.com/edit/angular-e2fnlm](https://stackblitz.com/edit/angular-e2fnlm?file=src%2Fapp%2Fexpansion-overview-example.html)

CSS solution works with **multiple Material Expansion Panels**
add **hideToggle** to mat-expansion-panel :

```
<mat-expansion-panel (opened)="panelOpenState = true"
                             (closed)="panelOpenState = false" hideToggle>

```

and add icon:

```
 <mat-expansion-panel-header>
            <mat-icon>add</mat-icon>

```