Change colour code to transparent

[killerford]

I'm using the tabbed mod and some guy posted the code and said just change the colour to what you want and that I might need to make to css files for both light and dark theme.

This is the code they posted

skin-tfh.css

.yui-navset .yui-content {
background:#ffffff;
border-top:5px solid #ADCCE1;
}

change the background element.

NOTE: you'll want to have a different CSS file for your dark and light styles..

The said that they made this code transparent so you don't need to have two different colours.. Can anyone tell me how to make this code transparent?