panel's defaultbutton is not working

Hi all, i have a small problem. I have submit button in my panel and i set it defaultbutton . My problem is that i dnt want to show this button i just want that when user press "Enter" from keyboard it fires that button click event. But if i set button's visibilty to false, this case does not work. but when i set display to true, this case scenario works. so i tried css.
here is my css:-
 .button
{
display:none;
}
But still it is showing the button on webpae, so please help me.
Thanks,
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