Overriding the background-color property in style1.css with no background-color style2.css

I have a style for #container in the main CSS for my site which works for all skins fin the site, except the one in which I want  #container to be semi-transparent. (See attached).
Overriding the background-image is easy enough with this one line of code in a secondary CSS:

#container {background-image: url(../images/Opacity60.png)}

The problem is that the background color property from the main code perseveres.  I tried getting rid of it by adding: "bakground-color: none;"   but  that isn't a valid property and it doesn't work.

The object here of course is to never have to change the html by adding a separate #container2 style, so how do I do this just within CSS?

Thanks!

JohnStart Free Trial

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#container {
	width: 890px;
	height: auto;
	font-family: "Gill Sans MT";
	font-size: 16px;
	margin: 0 auto;
	float: left;
	line-height: 24px;
	background-color: #FFFFFF;
	background-image: url(../images/CowSpotsWatermark_v4_wShad.jpg);
    }