You can add these sample codes on Frontier Options -> Custom CSS

#slider {
   background-color: #FFF;
}

.bjqs .bjqs-heading {
   background-color: #FFF;
}

.bjqs .bjqs-descript {
   background-color: #FFF;
}

For changing other elements, have a look a this:
https://ronangelo.com/use-firebug-to-modify-wordpress-theme-css/