How Do You Make block_background Transparent?

[MikalMirkas]

Title.
http://www.vbulletin.com/docs/html/stylevars_dictionary_blocks

[Attitude5ire]

Using opacity tag.
opacity:0.8;
filter:alpha(opacity=80);

You need to add it to additional CSS. But mind you if you background is white and adding any opacity to blocks on it are jus going to be faded look, which can be done using a faded gradient.

[ViperE-mpire]

Open the Style Variables for your skin. open the Block Background variable.
Click on the color box for the background.
Select the clear dotted box in the top left hand corner of the box that pops up.

[setishock]

Or simply just type transparent in where the color data would go and save your work.