No you cannot to my knowledge. Remember the RLM is just that, a layout maker. Although it has many excellent features added to it to create great looking website prototypes it will not allow you to alter the html within the application. I do know that they are working on a Responsive Site Designer that will have some of these features included in it. The developers and CC Staff are working extremely hard to get this completed so stay tuned
background-color: rgba(222, 19, 19, .6);
background-color: rgba(222, 19, 19, .65);
Would it be ok if I put the background image where the color is in both?
No you don't ever want to make changes to any of the css files that RLM exports as they will be overwritten every time you export your project. This is why you want to make a custom.css file and make all your modifications there. Once you have located the row, column, subgrid, subgrid row, or subgrid column you can apply the same method of adding an image to the background.
I have not tried to add an image to the body grid yet so I am not sure how it would respond, maybe someone else will chime in here with a solution to that issue. I am sure there is a way.
https://www.youtube.com/channel/UCL8qVv … ttneYaMSJA