Idea found and visualized here:
http://starwarsdof.motionsforum.com/forum.htm

(It's the black boxes that you can sort of see the brushed medal background coming through).

List of things I've tried but did not work:

Code:

td.row1{
  background-color: rgba(0, 0, 0, 0.6);  /* FF3+, Saf3+, Opera 10.10+, Chrome, IE9 */
            filter:  progid:DXImageTransform.Microsoft.gradient(startColorStr='#99000000',EndColorStr='#99000000'); /* IE6,IE7 */
        -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorStr='#99000000',EndColorStr='#99000000')"; /* IE8 */
-moz-box-shadow: 0px 0px 4px #1DC0FB; /* FF3.5+ */
  -webkit-box-shadow: 0px 0px 4px #1DC0FB; /* Saf3.0+, Chrome */
          box-shadow: 0px 0px 4px #1DC0FB; /* Opera 10.5, IE 9 */
}
td.row2{
  background-color: rgba(0, 0, 0, 0.6);  /* FF3+, Saf3+, Opera 10.10+, Chrome, IE9 */
            filter:  progid:DXImageTransform.Microsoft.gradient(startColorStr='#99000000',EndColorStr='#99000000'); /* IE6,IE7 */
        -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorStr='#99000000',EndColorStr='#99000000')"; /* IE8 */
-moz-box-shadow: 0px 0px 4px #1DC0FB; /* FF3.5+ */
  -webkit-box-shadow: 0px 0px 4px #1DC0FB; /* Saf3.0+, Chrome */
          box-shadow: 0px 0px 4px #1DC0FB; /* Opera 10.5, IE 9 */
}
td.row3{
  background-color: rgba(0, 0, 0, 0.6);  /* FF3+, Saf3+, Opera 10.10+, Chrome, IE9 */
            filter:  progid:DXImageTransform.Microsoft.gradient(startColorStr='#99000000',EndColorStr='#99000000'); /* IE6,IE7 */
        -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorStr='#99000000',EndColorStr='#99000000')"; /* IE8 */
-moz-box-shadow: 0px 0px 4px #1DC0FB; /* FF3.5+ */
  -webkit-box-shadow: 0px 0px 4px #1DC0FB; /* Saf3.0+, Chrome */
          box-shadow: 0px 0px 4px #1DC0FB; /* Opera 10.5, IE 9 */
}

td.row3Right,td.spaceRow {
  background-color: rgba(0, 0, 0, 0.6);  /* FF3+, Saf3+, Opera 10.10+, Chrome, IE9 */
            filter:  progid:DXImageTransform.Microsoft.gradient(startColorStr='#99000000',EndColorStr='#99000000'); /* IE6,IE7 */
        -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorStr='#99000000',EndColorStr='#99000000')"; /* IE8 */
-moz-box-shadow: 0px 0px 4px #1DC0FB; /* FF3.5+ */
  -webkit-box-shadow: 0px 0px 4px #1DC0FB; /* Saf3.0+, Chrome */
          box-shadow: 0px 0px 4px #1DC0FB; /* Opera 10.5, IE 9 */
}

- Works for ForumBody Line, but not for the Table Rows.

https://help.forumotion.com/tricks-tips-f32/to-make-the-cells-translucent-t137.htm
- Absolutely no difference, just black boxes (and that's an official Forummotion Tutorial)

I've set the color to black. I want the forums to show a picture through an 80% black row color, just like in the above example forum (the star wars one).

Using PHPBB3
http://mytestforum.ohmyforum.net <-My skin test forum, leaving it with the first code in so you can see it.

I fixed it myself. Tutorial is definitely wrong.

Code:

li.row {
-moz-border-radius : 10px;
-webkit-border-radius : 10px;
background-color: #000000;
 background-color: rgba(0, 0, 0, 0.6);  /* FF3+, Saf3+, Opera 10.10+, Chrome, IE9 */
            filter:  progid:DXImageTransform.Microsoft.gradient(startColorStr='#99000000',EndColorStr='#99000000'); /* IE6,IE7 */
        -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorStr='#99000000',EndColorStr='#99000000')"; /* IE8 */
-moz-box-shadow: 0px 0px 4px #1DC0FB; /* FF3.5+ */
  -webkit-box-shadow: 0px 0px 4px #1DC0FB; /* Saf3.0+, Chrome */
          box-shadow: 0px 0px 4px #1DC0FB; /* Opera 10.5, IE 9 */
 }


Best if viewed in FireFox.