Custom color for each Trailer box
Hi, I'm new here! Hope my Thread is in the proper section. So, my question is related with the Trailer box item. I've put some Trailer boxes at the front page instead your default portfolio / blog suggestions. They look pretty well, each of them has an individual picture and link to the certain page, but I want to customize the color box behind the text on the picture. Now all of the color boxes has one color, wich is the default for this kind of item. As I understand, I could customize the vision of this items by typing a custom CSS code in the customisation row of the item options, but I don't know how and what to type. Also as I understand, these customizations are temporal and they will gone when the theme begins to update. I don't have a child theme, and to be honest I can't inderstand how to create it, so is there a way to modify the custom codes every time after the theme is updated. Thanks in advance 
Comments
sorry but the trailer box does not have any custom css field, it only has a custom class field.
Please send a link to this page.
thanks