How to change my form background?

I have changed my form background, it looks fine on the screen, but when I publish it is something different.  I would like to have a transparent background, but it will not let me do this....WHY NOT?

You need to add this custom CSS code to make the form transparent.

.supernova { 
background: transparent !important;
} 

Here's a guide on how to insert CSS on the form: How-to-Inject-Custom-CSS-Codes.

On your webpage, you'll see the black background because the form is embedded on the container that has a black background. In order to fix that, please add this CSS code on the stylesheet of your website.

#stacks_in_75911_page7 { 
background-color: transparent !important;
} 

Hope that works. Thanks!