@alphaxyz:
1. For background in slider content with 50% opacity, you can add the following css in “Appearance => Customize => Theme Options => Custom CSS Options” box:
#feature-slider .entry-container { background-color: rgba(0, 0, 0, .5); }
2. To change promotion headline background color, you can change the color code in the following css and then add it in “Appearance => Customize => Theme Options => Custom CSS Options” box:
#promotion-message { background-color: #eee; }
but if you want to add background image then it will be as:
#promotion-message { background-image: "your image url"; }