Hi! I have been adding CSS to my den, but the only code I am struggling with getting to work is the foreground/scrolling bar? (idk what it's called haha!)

This is the code I have been attempting to use. Help would be greatly appreciated. Thank you!!

.col-md-9.col-xs-12 {
background: #556657 !important;
min-height: 800px !important;
padding-top: 25px;
padding-bottom: 25px;
}