Hi,
You can create CustomControl. Then customize it as you want. For example:
<UserControl x:Class="RibbonControls.CustomControl1View"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:ui="clr-namespace:RibbonControls"
xmlns:extensions="clr-namespace:ArcGIS.Desktop.Extensions;assembly=ArcGIS.Desktop.Extensions"
mc:Ignorable="d"
d:DesignHeight="300" d:DesignWidth="300"
d:DataContext="{Binding Path=ui.CustomControl1ViewModel}">
<UserControl.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<extensions:DesignOnlyResourceDictionary Source="pack://application:,,,/ArcGIS.Desktop.Framework;component\Themes\Default.xaml"/>
</ResourceDictionary.MergedDictionaries>
</ResourceDictionary>
</UserControl.Resources>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Label Content="My Combobox" />
<ComboBox Grid.Row="1" />
</Grid>
</UserControl>
It will look like this:
I have modified RibbonControls sample