The default opaque panel on top of gnome3 is like eating milk n chala curry.
The /usr/share/gnome-shell/theme/panel-border.svg is the main file to be changed to change its appearance.
Now wake the gimp expert in you
open the file /usr/share/gnome-shell/theme/panel-border.svg in gimp
must be root to do it
sudo gimp /usr/share/gnome-shell/theme/panel-border.svg
modify the file as you wish
here i deleted the whole image
ctrl + a
Del
then took the brush tool choose colour black (default)
set Opacity to 52
made the brush image large enough to cover the full image
painted once in the image
then choose orange colour,
set Opacity to 100
painted a line in the bottom, this will appear as the bottom border.
saved it as
panel-border.png
because in gimp does not support saving a file in .svg format.
Also i don't know whether svg can handle alpha channel.
now the pic will look like as shown
Now open up the file /usr/share/gnome-shell/theme/gnome-shell.css
/usr/share/gnome-shell/theme/gnome-shell.css
goto the section
#panel {
color: #ffffff;
background-color: black;
border-image: url("panel-border.png") 1;
font-size: 8.5pt;
height: 1.86em;
}
change the line border-image: url("panel-border.svg") 1;
to
border-image: url("panel-border.png") 1;
save the file
reload the gnome3 desktop by hitting
Alt+F2
then enter
r
hit
Enter--Happy Hacking 
