[napy8gen]

You can define new css class in main css>additional css definition.

.transparent{
filter: alpha(opacity=70); /* ie */
-moz-opacity: .7; /* mozilla */ }

apply it to any layout wrapper in the header template. that depends on your design code.
style manager> style namer> common templates> header

if in the header template the design start with table, you can call the class like this.

<table class="transparent">

if start with div

<div class="transparent">

In Main CSS page background property empty it or put value "transparent".