In Form Customize you can design form as much as your choice.
You can set background color, background filter on this section. There have many kinds of background filter like Blur, Brightness, Contrast, Grayscale, Invert, Opacity, Sepia, Saturate.
In this step you can set border color, width, radius.There have different types of border. Such as solid, dotted, dashed,double.
By Padding properties you can generate space around of content.
4. Margin :
By Margin properties you can generate space around of background.
You can set background shadow by using this property