Maybe try the color bulb template, since it has the popup for on/off and slider for level if no color or CT attributes available.
The defaults are to use the CSS property "cover" for background-size and position of "center center" which means the center vertically and horizontally will be used to place the background image and the cover command means it will be sized to fit both horizontally and vertically without stretching.
The drop shadow is there to make sure white or black text doesn't disappear if the user selects the same background color. However, for advanced users, a css editor will probably make its debut in the next release that will allow further customization.
That's what its there for. And of course, sections of it can be shared like the customColors section for your templates.
