I've a layer containing a SWF that I want to be visible on top of another text layer in CSS.

Trouble is that the layer appears like a white block with my SWF in it over the text. I'd like the white in my SWF layer to be transparent so I can see the text beneath it.
Is this possible in CSS?

You can use absolute positioning and the z-index property to accomplish that.

z-index allows stacking of elements on top of one another. The higher the z-index, the closer to the foreground the object becomes (the default for all elements is 0).

http://www.w3schools.com/css/pr_pos_z-index.asp

Change your publish settings in Flash so that it generates the SWF as 'windowless transparent'. That will get rid of the white block.
Then, if you still need it, you can use Adam's solution.

Thanks, tried the z-index (below). Didn't work.
My SWF layer is layer13 and my text layer is layer1.
I want my text to appear over my SWF.

I have made my SWF transparent. (param name="wmode" value="transparent") etc.

#layer1 { font-family: Helvetica, Geneva, SunSans-Regular, sans-serif, "Arial Narrow"; font-size: 8pt; font-weight: normal; height: 390px; width: 240px; left: 570px; top: 120px; position: absolute; visibility: visible; z-index=1; }
@font-face{ font-family: "Arial Narrow"; font-size: 10; font-variant: normal; }

#layer12 { height: 80px; width: 110px; left: 420px; top: 430px; position: absolute; visibility: visible; z-

index=2; }
#layer2 { height: 50px; width: 260px; left: 575px; top: 552px; position: absolute; visibility: visible; z-

index=3; }
#layer3 { height: 701px; width: 913px; left: 0; top: 0; position: absolute; visibility: visible; z-index=4; }
#layer5 { height: 100px; width: 310px; left: 460px; top: 50px; position: absolute; visibility: visible; z-

index=5; }
#layer6 { height: 60px; width: 115px; left: 245px; top: 60px; position: absolute; visibility: visible; z-index=6;

}
#layer7 { height: 60px; width: 115px; left: 134px; top: 115px; position: absolute; visibility: visible; z-

index=7; }
#layer8 { height: 60px; width: 115px; left: 71px; top: 201px; position: absolute; visibility: visible; z-index=8;

}
#layer9 { height: 60px; width: 115px; left: 72px; top: 304px; position: absolute; visibility: visible; z-index=9;

}
#layer10 { height: 60px; width: 115px; left: 135px; top: 390px; position: absolute; visibility: visible; z-

index=10; }
#layer11 { height: 60px; width: 115px; left: 246px; top: 440px; position: absolute; visibility: visible; border-

width: 0; border: 0pt z-index=11; }
#layer4 { height: 260px; width: 340px; left: 230px; top: 160px; position: absolute; visibility: visible; z-index=12; }

#layer13 { height: 120px; width: 120px; left: 780px; top: 50px; position: absolute; visibility: visible; z-index=13; }

OMG

First of all, absolutely positioning ALL of those elements ( they are NOT LAYERS) is just not necessary and it's going to cause you a lot of problems.

If you want your SWF to be on top, give it a z-index of 200. However I suspect there are other things going on there that is causing your problem.

Whether you want to call them layers or divs, give them each a name. Seriously, it will make things so much easier for you. I'm having a hard time figuring out what's going on in your code; that must be a pain to work with? They don't have to be good names, swf and textUnderSwf.

If the first div goes on the top, and the next one below it, or basically the elements aren't covering each other, you don't need to assign them a z-index. That only comes into play when two elements could cover each other.

Set visibility: visible; at the html level. That will make it like a default, so you don't have to repeat it in all of your rules.

visibility: visible isn't necessary, as everything is visible by default anyway.
The stacking order is from the bottom UP. It would be better to use the normal document flow, floats and then only use absolute positioning where ..well absolutely necessary.