Example to set widget gradient background color
See What’s NNN of “.testimonials-widget-testimonialsNNN”? for NNN identification. Then write CSS like the following change the color behind the widget to a light gradient gold.
.testimonials-widget-testimonials3 { background-image: linear-gradient(to bottom right, #FFEF87 0%, #EFEFEF 100%); }
A special thanks to inode86 for this suggestion.