How to set backgroud opacity in CMS

[edyy]

To be more clear I will try to explain what I whant to do and what i did until now. I want the backgroud from sections ( the white color on default theme) to be transparet to set an opacity level, something like in this example from the tutorial http://www.w3schools.com/Css/css_image_transparency.asp. I tried to add the opacity 0.6 to the body_background stylevar but without any succes. Can you help me to make that possible. The test site is test.games-area.ro and the color of the css i want to change will be set to yellow for a better usage.

Thanks!