bloxstrap/Bloxstrap/UI/Elements/Controls/Expander.xaml

<UserControl x:Class="Bloxstrap.UI.Elements.Controls.Expander"
             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="http://schemas.lepo.co/wpfui/2022/xaml"
             xmlns:local="clr-namespace:Bloxstrap.UI.Elements.Controls"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800"
             x:Name="Control">
    <Expander VerticalAlignment="Top" IsExpanded="{Binding IsExpanded, ElementName=Control}" Content="{Binding InnerContent, ElementName=Control}">
        <Expander.Header>
            <Grid>
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="Auto" />
                    <ColumnDefinition Width="Auto" />
                </Grid.ColumnDefinitions>
                <ui:SymbolIcon Grid.Column="0" Margin="0,0,8,0" VerticalAlignment="Center" Symbol="{Binding HeaderIcon, ElementName=Control}" />
                <TextBlock Grid.Column="1" VerticalAlignment="Center" Text="{Binding HeaderText, ElementName=Control}" />
            </Grid>
        </Expander.Header>
    </Expander>
</UserControl>