Godot - Change progress bar color and transparency

GDScript to change progress bar color and transparency.

It is possible to change the color and transparency of progress bars using StyleBoxFlat.
By specifying "fill" and "background" in add_theme_stylebox_override(), you can enable changing the style of the bar and background style.
Change the color and transparency with the "bg_color" property.

# bar
var bar = StyleBoxFlat.new()
add_theme_stylebox_override('fill', bar)
bar.bg_color = Color('#00ff7f' , 0.5)

# background
var bg = StyleBoxFlat.new()
add_theme_stylebox_override('background', bg)
bg.bg_color = Color('#696969',1)