<FORM>
<INPUT ID="counter1" STYLE="position:relative; top:'0px'" TYPE="button" VALUE="Move Button" 
onclick="document.getElementById('counter1').style.top = '15px';">
</FORM>

That renders like this:

<FORM>
<INPUT ID="counter2" STYLE="position:relative; top:0" TYPE="button" VALUE="Move Button" 
onclick="document.getElementById('counter2').style.top = 15;">
</FORM>

And you can play with it as well:

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