fading background using CSS

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hi friends ,


i have two images

1) back.jpg
2) bar.gif



I want that when i press submit button then back.jpg comes to screen with 50% opacity and bar.gif opens in the center of that images to show that processing is occuring

Can anyone help me out

[Kor]

But when you submit, you will also change the session, won't you? so that you can not use javascript.

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When i pres submit button , the processing was taking 8-9 seconds
so just wanted to show some processing screen but

i found on internet using CSS opacity function and solved it