WPF: How to make a button background transparent

I want to know how to set a wpf button background to transparent.

开发者_开发问答thank you

<Button Background="Transparent"/>

Transparency Declaratively

<Button Background="Transparent"/>

Transparency programatically

this.btnTransparent.Background = Brushes.Transparent;

Semi-transparency declaratively

Opacity="0.5"

Semi-transparency programmatically

this.Opacity = 0.5;