MainWindow.xaml

<Window x:Class="AppearanceCustomization.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:AppearanceCustomization"
        xmlns:syncfusion="http://schemas.syncfusion.com/wpf"
        xmlns:system="clr-namespace:System;assembly=mscorlib"
        xmlns:skinmanager ="clr-namespace:Syncfusion.SfSkinManager;assembly=Syncfusion.SfSkinManager.WPF"
        skinmanager:SfSkinManager.VisualStyle="MaterialLight"
        mc:Ignorable="d"
        Title="AppearanceCustomization Demo"
        Icon="App.ico"
        WindowStartupLocation="CenterScreen">
    <Window.DataContext>
        <local:SchedulerViewModel/>
    </Window.DataContext>

    <Window.Resources>
        <ObjectDataProvider x:Key="schedulerViewTypes" MethodName="GetValues"
                            ObjectType="{x:Type system:Enum}">
            <ObjectDataProvider.MethodParameters>
                <x:Type  Type="{x:Type syncfusion:SchedulerViewType}"/>
            </ObjectDataProvider.MethodParameters>
        </ObjectDataProvider>
        
        <local:SubjectToImageSourceConverter x:Key="subjectToImageConverter"/>

        <DataTemplate x:Key="appointmentTemplate">
            <StackPanel Background="{Binding Background}"  
                        VerticalAlignment="Stretch" 
                        HorizontalAlignment="Stretch"
                        Orientation="Horizontal">
                <Image x:Name="Image"
                        VerticalAlignment="Center"
                       Height="30"
                       Width="15"
                       Margin="5,0"
                        Source="{Binding Converter={StaticResource subjectToImageConverter}, Path=EventName}">
                    </Image>
                    <TextBlock Margin="5"
                               VerticalAlignment="Center"
                               Text="{Binding EventName}" 
                               TextTrimming="CharacterEllipsis"
                               TextWrapping="Wrap"
                               TextAlignment="Left"
                               FontWeight="Bold"/>
            </StackPanel>
        </DataTemplate>

        <DataTemplate x:Key="allDayAppointmentTemplate">
            <StackPanel Background="{Binding Background}"  
                        VerticalAlignment="Stretch" 
                        HorizontalAlignment="Stretch"
                        Orientation="Horizontal">
                <Image x:Name="Image" 
                           VerticalAlignment="Top"
                           Height="20"
                           Width="15"
                           Margin="5,2,0,0"
                           Source="{Binding Converter={StaticResource subjectToImageConverter}, Path=EventName}">
                    </Image>
                    <TextBlock Margin="5"
                               HorizontalAlignment="Stretch" 
                               VerticalAlignment="Top"
                               Text="{Binding EventName}" 
                               TextTrimming="CharacterEllipsis"
                               TextWrapping="Wrap" 
                               FontWeight="SemiBold"/>
                </StackPanel>
        </DataTemplate>

        <DataTemplate x:Key="monthAppointmentTemplate">
            <StackPanel Background="{Binding Background}" 
                        VerticalAlignment="Stretch"
                        HorizontalAlignment="Stretch"
                        Orientation="Horizontal">
                <Image x:Name="Image" 
                       HorizontalAlignment="Center"
                       VerticalAlignment="Top"
                       Height="12"
                       Width="15"
                       Margin="5,2,0,0"
                       Source="{Binding Converter={StaticResource subjectToImageConverter}, Path=EventName}">
                </Image>
                <TextBlock Margin="5,2,0,0"
                           FontSize="10"
                           HorizontalAlignment="Stretch" 
                           Text="{Binding EventName}" 
                           TextTrimming="CharacterEllipsis"
                           TextWrapping="Wrap"
                           FontWeight="Heavy"/>
            </StackPanel>
        </DataTemplate>
    </Window.Resources>

    <Grid>
        <syncfusion:SfScheduler x:Name="Schedule"
                                ViewType="{Binding ElementName=viewTypeComboBox, Path=SelectedValue}" 
                                ItemsSource="{Binding Appointments}">
            
            <syncfusion:SfScheduler.MonthViewSettings>
                <syncfusion:MonthViewSettings AppointmentDisplayMode="Appointment"
                                              AppointmentTemplate="{StaticResource monthAppointmentTemplate}">
                </syncfusion:MonthViewSettings>
            </syncfusion:SfScheduler.MonthViewSettings>
            
            <syncfusion:SfScheduler.DaysViewSettings>
                <syncfusion:DaysViewSettings AppointmentTemplate="{StaticResource appointmentTemplate}"
                                             AllDayAppointmentTemplate="{StaticResource allDayAppointmentTemplate}"/>
            </syncfusion:SfScheduler.DaysViewSettings>
            
            <syncfusion:SfScheduler.TimelineViewSettings>
                <syncfusion:TimelineViewSettings AppointmentTemplate="{StaticResource appointmentTemplate}"/>
            </syncfusion:SfScheduler.TimelineViewSettings>
            
            <syncfusion:SfScheduler.AppointmentMapping>
                <syncfusion:AppointmentMapping StartTime="From"
                                               EndTime="To"
                                               Subject="EventName"
                                               AppointmentBackground="Background"
                                               IsAllDay="IsAllDay"/>
            </syncfusion:SfScheduler.AppointmentMapping>
        </syncfusion:SfScheduler>
        <StackPanel
            HorizontalAlignment="Right"
            VerticalAlignment="Top"
             Margin="0,20,25,0">
            <ComboBox x:Name="viewTypeComboBox" ItemsSource="{Binding Source={StaticResource schedulerViewTypes}}"
                                 SelectedIndex="2"  Width="100"/>
        </StackPanel>
    </Grid>
</Window>