How to change menu drop down background color

I would to know where are the images stored for JUX mega menu. I can't seem to link or find the folder where the images should be stored.
I believe I know where to css is located:

#js-mainnav.megamenu.white .childcontent-inner {
background-color: #FFF; <

---

I would like to add an image here, if this is the correct position *
border-radius: 0 0 5px 5px;
box-shadow: 0 0 6px rgba(76, 76, 76, 0.25);
left: -1px;
position: relative;
top: 1px;
}

The site is local and not online.
Thanks for any help.... Im new to JUX
Big5hot

Hi big5hot !
You can edit background the below:
example:
#js-mainnav.megamenu.white .childcontent-inner {
background-color: #FFF; <

Edit:
#js-mainnav.megamenu.white .childcontent-inner {
background-image: url('../image/demo.png')
Best Regards,
Huyen Tran