By applying this style you are setting the template for all buttons.
But there it is not defined how the content must be displayed.
Therefore the button seems to have disappeared.
<Window.Resources>
<Style TargetType="Button">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type Button}">
<ControlTemplate.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Background" Value="#733847"></Setter>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Background" Value="#3b1922"></Setter>
</Trigger>
<Trigger Property="IsPressed" Value="True">
<Setter Property="Background" Value="#592533"></Setter>
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
It is assumed that you just want to change the background when e.g. the mouse is over the button.
Here is how to accomplish that.
<Window.Resources>
<Style TargetType="Button">
<Style.Triggers>
<Trigger Property="IsMouseOver" Value="True">
<Setter Property="Background" Value="#733847"></Setter>
</Trigger>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Background" Value="#3b1922"></Setter>
</Trigger>
<Trigger Property="IsPressed" Value="True">
<Setter Property="Background" Value="#592533"></Setter>
</Trigger>
</Style.Triggers>
</Style>
</Window.Resources>
You should follow this tutorial in order to understand how WPF triggers work.
WPF - Triggers[
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