How do I make the image header on my form to go across the entire web page?

Another question (unrelated) that I have is how do I make the image header on my form to go across the entire web page?
Here is the link to the form: https://form.jotform.com/62612150564247
Video Cost Calculator:

|
|
|
| | |
|
|
|
| |
Video Cost Calculator:
Please click the link to complete this form. | |
|
|

Hello Munaz,

Please inject the following custom css code in your form to set the background image in form:

.supernova {

    background-image: url("http://webadvertisingexperts.com/wp-content/uploads/dental-video-marketing-image.jpg");

   background-repeat: repeat;

}

The following guide should help you how to inject custom css code in form:  https://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes 

Thank you!