Ubuntu – How to change web browser’s tab bar background color or image

Running Precise. I am tweaking the ambiance theme to my taste.
Yet I can't locate where I can modify the background color of the browser's tab bar (I suspect its value instruction to be somewhere in the gtk-widget or gtk-3 style files). See image:

Thanks in advance.

——————-EDIT–———————

Solution:

Edited the following files:

• /usr/share/themes/MyTheme/gtk-2.0/apps/chromium.rc ( style "chrome-gtk-frame"{ …})

• gtk.css

• gtkrc (gtk-2.0 folder / first line of style dark – background – ) :

style "dark"
{
    color["bg_color_dark"]  = "#303030"   #original was 3c3b37
    color["fg_color_dark"]  = "#dfdbd2"
    color["selected_fg_color_dark"] = "#ffffff"

fg[NORMAL]        = @fg_color_dark
fg[PRELIGHT]      = shade (1.15, @fg_color_dark)
fg[ACTIVE]    = @fg_color_dark
fg[SELECTED]      = @selected_fg_color_dark
fg[INSENSITIVE]   = shade (0.5, @fg_color_dark)

bg[NORMAL]        = @bg_color_dark
bg[ACTIVE]    = shade (0.8, @bg_color_dark)
bg[SELECTED]      = @selected_bg_color
bg[PRELIGHT]      = shade (1.0, "#4D4C48")
bg[INSENSITIVE]   = shade (0.85, @bg_color_dark)

text[NORMAL]      = @fg_color_dark
text[PRELIGHT]    = shade (1.15, @fg_color_dark)
text[SELECTED]    = @selected_fg_color_dark
text[ACTIVE]      = @fg_color_dark
text[INSENSITIVE] = mix (0.5, @bg_color, @bg_color_dark)

}

RESULT: