How to fix Eclipse's black background tooltip in Ubuntu

Insert the following into ~/.config/gtk-3.0/gtk.css

@define-color tooltip_bg_color #FFFFE1;
@define-color tooltip_fg_color #343434;
@define-color theme_tooltip_bg_color @tooltip_bg_color;
@define-color theme_tooltip_fg_color @tooltip_fg_color;

.tooltip {
    background-color:   @theme_tooltip_bg_color;
    color:              shade(@theme_tooltip_fg_color, 0.90);
    text-shadow:        none;
}
.tooltip * {
    background-color: @theme_tooltip_bg_color;
}

Bonus: to debug Eclipse (or any Gtk+ program), just launch it from the terminal with the following:

GTK_DEBUG=interactive /path/to/your/program