Style an Expander control

Question

Hi,

I am trying to style an expander control. But i am unable to style a certian area of the control. The figure can be seen in this post.(figure 1)

http://stackoverflow.com/questions/2889778/wpf-expander-button-styled-so-it-is-inside-expander-header

I want the circle color to be that of my datagrid. How can i accomplish that in WPF.