How to make the background image fixed and no repeated?

hi, I already have finished creating a customer feedback form. I have chosen theme, which has a image background. in Build section, picture doesn't change and while scrolling moves just form, when i have finished form, while scrolling picture gets multiple and there's seen dividing line between pictures. i'm sending you screenshot for you to better understand my problem.

how can we change that ? 

thank you! 

thank you! 

Hello,

I inserted the below CSS in your Custom CSS field and it should work now as you intended:

.supernova {

background: url("http://www.jotform.com/uploads/EltonCris/form_files/keyboard-498396_12801.png") no-repeat center center fixed;

-webkit-background-size: cover;

-moz-background-size: cover;

-o-background-size: cover;

background-size: cover;

} 

Let us know if you have any further questions.

Thank you!