How to change my Group-box style

Question

So this is my GroupBox:

<GroupBox 
    Header="My header"
    Background="Transparent"
    Foreground="Gainsboro"
    BorderBrush="Gainsboro" />

And i have several things that i want to change/issues:

1. The Foreground is still in black although i have changed it.
2. My boder around the Header: i want to remove it in order to achieve this kind of style (the header is over the border):

3. All header is with upper case.

Edit:

After add the style that user @mm8 suggested, this is the results:

Why i can see duplicate border ?

Answer 1

Create your own set of controls to have full control, similar to this:

<Grid Width="100" Height="200" Background="DodgerBlue">
    <Grid.RowDefinitions>
        <RowDefinition Height="20"/>
        <RowDefinition Height="*"/>
    </Grid.RowDefinitions>

    <Border BorderThickness="1" BorderBrush="Gainsboro">
        <TextBlock Foreground="Gainsboro">Header</TextBlock>
    </Border>

    <Border Grid.Row="1" BorderThickness="1" BorderBrush="Gainsboro">
        <!--Content-->
    </Border>
</Grid>