Two implicit styles — the bar and the tray it sits in — plus a set of styles for the controls that go inside one, which WPF applies for you through its own style keys.

<ToolBarTray>
    <ToolBar>
        <Button Content="New" />
        <Button Content="Open" />
        <Separator />
        <ToggleButton Content="Bold" IsChecked="True" />
        <ToggleButton Content="Italic" />
    </ToolBar>
</ToolBarTray>

Styles/Controls.xaml applies MahApps.Styles.ToolBar and MahApps.Styles.ToolBarTray, so the quick start is the whole setup.

Controls inside a toolbar are restyled for you

A ToolBar re-styles its children through eight style keys that WPF looks up by name. MahApps fills in six of them:

Note rows three and four: a CheckBox or a RadioButton dropped into a toolbar is given the toggle button style. It loses its box or its dot and becomes a button that stays pressed:

All four items in that figure are different control types, and three of them look identical because three keys point at the same style.

ToolBar.MenuStyleKey and ToolBar.SeparatorStyleKey are the two MahApps leaves alone, so a Menu or a Separator inside a toolbar keeps WPF's own look. The separator is a plain vertical line, which fits; a Menu is worth styling yourself if you put one there.

Background belongs on the tray

<Border x:Name="Border"
        Background="{DynamicResource MahApps.Brushes.Transparent}"
        BorderBrush="{DynamicResource MahApps.Brushes.Transparent}"
        BorderThickness="1"
        CornerRadius="2">

<ToolBarTray Background="{DynamicResource MahApps.Brushes.Gray10}">
    <ToolBar>
        <!-- items -->
    </ToolBar>
</ToolBarTray>

MahApps.Styles.ToolBarTray is one setter — a Background of MahApps.Brushes.Window.Background — so that is the only place the colour comes from unless you change it.

To colour a single bar rather than the whole tray, base a style on MahApps.Styles.ToolBar and replace the template, or put the bar in a tray of its own.

The drag grip

The dotted grip on the left is a Thumb with a SizeAll cursor, and it is what lets the user drag a bar to another row of the tray. ToolBarTray.IsLocked collapses it:

<ToolBarTray IsLocked="True" />

The template also disables the grip while the overflow popup is open, so a bar cannot be dragged out from under its own menu.

Overflow

When the bar is narrower than its items, the ones that do not fit move into a popup behind a chevron at the right-hand end. That button is MahApps.Styles.ToggleButton.ToolBarOverflow; it is disabled while HasOverflowItems is false, so it only lights up when there is something to show.

The popup itself is a bordered panel in MahApps.Brushes.Control.Background with a ToolBarOverflowPanel that wraps at 200 units. Mark an item as always overflowing, or never, with WPF's own attached property:

<Button Content="Rarely used" ToolBar.OverflowMode="Always" />

The Windows 10 and the WinUI look

WPF has no CommandBar, and the ToolBar is the same thing: a row of commands with the rest behind the dots. MahApps.Styles.ToolBar.Win10 and MahApps.Styles.ToolBar.WinUI give it the look of the CommandBar of UWP and of WinUI 3, and the Win10 and the WinUI set apply them by type, together with MahApps.Styles.ToolBarTray.Win10 and .WinUI.

<ToolBar ToolBarTray.IsLocked="True">
    <Button ToolTip="Add">
        <mah:FontIcon Glyph="&#xE710;" />
    </Button>
    <Button>
        <StackPanel Orientation="Horizontal">
            <mah:FontIcon Glyph="&#xE74E;" />
            <TextBlock Margin="8 0 0 0" VerticalAlignment="Center" Text="Save" />
        </StackPanel>
    </Button>
    <Separator />
    <ToggleButton IsChecked="True" ToolTip="Bold">
        <mah:FontIcon Glyph="&#xE8DD;" />
    </ToggleButton>
    <Button Content="Delete" ToolBar.OverflowMode="Always" />
</ToolBar>

The bar carries the style keys for its items in its own resources, so a Windows 10 bar has Windows 10 buttons even in a window of the default set. Seven of the eight keys are filled in. The separator gets a look of its own here, MahApps.Styles.Separator.ToolBar.Win10 and .WinUI, and only MenuStyleKey stays empty.

A few things differ from the Metro bar. The bar takes the Background it is given. The dots are only there while something has gone into the drop-down, as with the CommandBar, instead of sitting there disabled. And the drop-down is a list: the commands stand one under the other, each as wide as the widest, where the panel WPF has there would put short ones side by side. It opens below the dots and ends where they end.

An icon and a label are content like any other, so a label next to the icon is a StackPanel. There is no label below the icon the way AppBarButton draws one, and no IsOpen that folds the labels in and out.

The colours are in the theme as MahApps.Brushes.ToolBar.Win10.* and MahApps.Brushes.ToolBar.WinUI.*: Background, Foreground, BackgroundOpen and BorderBrushOpen (WinUI only), OverflowBackground, OverflowBorderBrush, Separator, Gripper, ButtonBackground, ButtonForeground with its PointerOver, Pressed and Disabled steps, and the ToggleButton…Checked steps of a checked button.

Related

The toolbar button styles are variants of the ones on the Buttons page, and the text box and combo box inside a toolbar are the ordinary TextBox and ComboBox styles.