https://stackoverflow.com/questions/2607508/how-to-control-docking-order-in-winforms
Go to View -> Other windows -> document outline.
In that window drag the controls so the docking is as you like it to be.
The order is in reverse order.
this.pnlNavigator.BackColor = System.Drawing.Color.White;
1 this.pnlNavigator.Controls.Add(this.ttlMemberWebsiteSystemStep);
2 this.pnlNavigator.Controls.Add(this.ttlProgramSystemStep);
3 this.pnlNavigator.Controls.Add(this.ttlGeneralStep);
After adjustment, the order of adding background is reverse order.
First display 3, then display 2, then display 1.