How to carry out a CSS background clip

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CSS

Hi,

I have a sprite image as a background on a validation message. It has a picture that I want to show with varying messages in the validation box. The longer the message, the longer down the sprite is stretched and with long text it reveals other parts of the sprite that I would like to be hidden.

How do I clip the background image using CSS so it only stretches down so far then stops, therefore not showing any of the other unwanted sprites? Bear in mind, I cant use any other DIV tags or anything else at this point.

Thanks in advance!