Customize

Hi, I want to customize the background color of specific pages, and I think I have to use some codes and I don´t know how to do it. I choose a general background color (beige) for all the frontpage (I did it with the theme and colors tools). BUT in some other pages I don´t want that color.So, how can I change it? I tried with this that I found somewhere on the web: body.page-id-5372 .site-content-contain{background-color:000; color: white;} First it said that I needed a higher level of permission to customize it. But I´m the administrator, son I don´t understand. Then I tried again, and that message didn´t show up again, BUT it doesn´t do anything neither. So, I need help please :(