`<mat-toolbar>` is a container for headers, titles, or actions.

<!-- example(toolbar-overview) -->

### Single row

In the most situations, a toolbar will be placed at the top of your application and will only 
have a single row that includes the title of your application.

```html
<mat-toolbar>
  <span>My Application</span>
</mat-toolbar>
```

### Multiple rows

The Material Design specifications describe that toolbars can also have multiple rows. Creating
toolbars with multiple rows in Angular Material can be done by placing `<mat-toolbar-row>` elements
inside of a `<mat-toolbar>`.

```html
<mat-toolbar>  
  <mat-toolbar-row>
    <span>First Row</span>
  </mat-toolbar-row>
  
  <mat-toolbar-row>
    <span>Second Row</span>
  </mat-toolbar-row>
</mat-toolbar>
```

**Note**: Placing content outside of a `<mat-toolbar-row>` when multiple rows are specified is not
supported.

### Positioning toolbar content
The toolbar does not perform any positioning of its content. This gives the user full power to 
position the content as it suits their application.

A common pattern is to position a title on the left with some actions on the right. This can be
easily accomplished with `display: flex`:
```html
<mat-toolbar color="primary">
  <span>Application Title</span>
  
  <!-- This fills the remaining space of the current row -->
  <span class="example-fill-remaining-space"></span>
  
  <span>Right Aligned Text</span>
</mat-toolbar>
```
```scss
.example-fill-remaining-space {
  /* This fills the remaining space, by using flexbox. 
     Every toolbar row uses a flexbox row layout. */
  flex: 1 1 auto;
}
```

### Theming
The color of a `<mat-toolbar>` can be changed by using the `color` property. By default, toolbars
use a neutral background color based on the current theme (light or dark). This can be changed to 
`'primary'`, `'accent'`, or `'warn'`.  

### Accessibility
By default, the toolbar assumes that it will be used in a purely decorative fashion and thus sets
no roles, ARIA attributes, or keyboard shortcuts. This is equivalent to having a sequence of `<div>`
elements on the page.

Generally, the toolbar is used as a header where `role="heading"` would be appropriate.

Only if the use-case of the toolbar match that of role="toolbar", the user should add the role and
an appropriate label via `aria-label` or `aria-labelledby`.