PicView/src/PicView.Avalonia.Theme/Controls/Button.axaml

<ResourceDictionary xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Design.PreviewWith>
        <Button />
    </Design.PreviewWith>

    <ControlTheme x:Key="{x:Type Button}" TargetType="Button">

        <Setter Property="Button.Template">
            <ControlTemplate TargetType="Button">
                <ContentPresenter
                    Name="PART_ContentPresenter"
                    Padding="{TemplateBinding Padding}"
                    HorizontalContentAlignment="{TemplateBinding HorizontalContentAlignment}"
                    VerticalContentAlignment="{TemplateBinding VerticalContentAlignment}"
                    Background="{TemplateBinding Background}"
                    BorderBrush="{TemplateBinding BorderBrush}"
                    BorderThickness="{TemplateBinding BorderThickness}"
                    Content="{TemplateBinding Content}"
                    ContentTemplate="{TemplateBinding ContentTemplate}"
                    CornerRadius="{TemplateBinding CornerRadius}"
                    RecognizesAccessKey="True"
                    TextElement.Foreground="{TemplateBinding Foreground}" />
            </ControlTemplate>
        </Setter>

        <Style Selector="^.hover:pointerover /template/ ContentPresenter#PART_ContentPresenter">
            <Style.Animations>
                <Animation IterationCount="1" Duration=".35">
                    <KeyFrame>
                        <Setter Property="Background">
                            <SolidColorBrush Color="{StaticResource SecondaryBackgroundColor}" />
                        </Setter>
                    </KeyFrame>
                    <KeyFrame Cue="1">
                        <Setter Property="Background">
                            <SolidColorBrush Color="{DynamicResource AccentColor}" />
                        </Setter>
                    </KeyFrame>
                </Animation>
            </Style.Animations>
            <Setter Property="Background" Value="{DynamicResource AccentColor}" />
        </Style>
        <Style Selector="^.altHover:pointerover /template/ ContentPresenter#PART_ContentPresenter">
            <Style.Animations>
                <Animation IterationCount="1" Duration=".35">
                    <KeyFrame>
                        <Setter Property="Background">
                            <SolidColorBrush Color="{StaticResource SecondaryBackgroundColor}" />
                        </Setter>
                    </KeyFrame>
                    <KeyFrame Cue="1">
                        <Setter Property="Background">
                            <SolidColorBrush Color="{StaticResource BackgroundHoverColor}" />
                        </Setter>
                    </KeyFrame>
                </Animation>
            </Style.Animations>
            <Setter Property="Background" Value="{StaticResource BackgroundHoverColor}" />
        </Style>
        <Style Selector="^.alphaHover:pointerover /template/ ContentPresenter#PART_ContentPresenter">
            <Style.Animations>
                <Animation IterationCount="1" Duration=".35">
                    <KeyFrame>
                        <Setter Property="Background">
                            <SolidColorBrush Color="Transparent" />
                        </Setter>
                    </KeyFrame>
                    <KeyFrame Cue="1">
                        <Setter Property="Background">
                            <SolidColorBrush Color="{StaticResource AltBackgroundHoverColor}" />
                        </Setter>
                    </KeyFrame>
                </Animation>
            </Style.Animations>
            <Setter Property="Background" Value="{StaticResource AltBackgroundHoverColor}" />
        </Style>
        <Style Selector="^.hover:pressed  /template/ ContentPresenter#PART_ContentPresenter">
            <Setter Property="Background" Value="{DynamicResource SecondaryAccentColor}" />
        </Style>
        <Style Selector="^.alphaHover:pressed  /template/ ContentPresenter#PART_ContentPresenter">
            <Setter Property="Background" Value="{DynamicResource SecondaryAccentColor}" />
        </Style>
        <Style Selector="^:disabled">
            <Setter Property="Opacity" Value="{DynamicResource ThemeDisabledOpacity}" />
        </Style>
    </ControlTheme>
</ResourceDictionary>