How to change menu opacity in RokoPhoto

By default Rokophoto's menu is transparent before scroll and gains a solid background after scroll. You could always have a background by adding the following code snippet to your childtheme's style.css/custom.css

Additionally if you do not have a childtheme you could install the plugin called "Advanced CSS Editor" and add the following snippet to it by going to Appearance->Customize->Advanced CSS Editor:

.main-navigation ul ul{background: #222222;}
.navbar-default{background: #222222;}