@ ilia-choly прав, но если вы хотите, чтобы он работал и в некоторых старых браузерах, вы можете попробовать jQuery, а именно:
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.2/jquery.js"></script>
<script>
/* Config */
targetElement = 'center a'; /* Select the element(s) you want to fade in and out */
fadedOpacity = .3; /* The opacity value you like for your faded state */
animDuration = 250; /* The duration in ms for the fade animations, smaller is faster */
/* This block runs once the document loads to bind the plugin behaviour to your target */
$(function(){
$(targetElement).fadeInOnHover(fadedOpacity, animDuration);
// ... You can bind the behaviour to other elements here if you need to, e.g:
// $('div.new-target').fadeInOnHover(fadedOpacity, animDuration);
});
/* This small jQuery plugin behaviour can be applied to any element */
$.fn.fadeInOnHover = function(fadedOpacity, animDuration) {
$(targetElement)
.fadeTo(0, fadedOpacity)
.bind('mouseover',function(){
$(this).fadeTo(animDuration, 1);
})
.bind('mouseout',function(){
$(this).fadeTo(animDuration, fadedOpacity);
})
;
};
</script>