Simple Tooltip with jQuery and CSS

Sample

Your Link Key Word This will show up in the tooltip

The Markup – HTML showing how to use
<a href="#" class="tip_trigger">Your Link Key Word <span class="tip">This will show up in the tooltip</span></a>


The CSS
.tip {
    color: #fff;
    background:#1d1d1d;
    display:none; /*--Hides by default--*/
    padding:10px;
    position:absolute;    z-index:1000;
    -webkit-border-radius: 3px;
    -moz-border-radius: 3px;
    border-radius: 3px;
}

The Javascript/Jquery
$(document).ready(function() {
    //Tooltips
    $(".tip_trigger").hover(function(){
        tip = $(this).find('.tip');
        tip.show(); //Show tooltip
    }, function() {
        tip.hide(); //Hide tooltip
    }).mousemove(function(e) {
        var mousex = e.pageX + 20; //Get X coodrinates
        var mousey = e.pageY + 20; //Get Y coordinates
        var tipWidth = tip.width(); //Find width of tooltip
        var tipHeight = tip.height(); //Find height of tooltip

        //Distance of element from the right edge of viewport
        var tipVisX = $(window).width() - (mousex + tipWidth);
        //Distance of element from the bottom of viewport
        var tipVisY = $(window).height() - (mousey + tipHeight);

        if ( tipVisX < 20 ) { //If tooltip exceeds the X coordinate of viewport
            mousex = e.pageX - tipWidth - 20;
        } if ( tipVisY < 20 ) { //If tooltip exceeds the Y coordinate of viewport
            mousey = e.pageY - tipHeight - 20;
        }
        //Absolute position the tooltip according to mouse position
        tip.css({  top: mousey, left: mousex });
    });
});

reference

http://www.sohtanaka.com/web-design/simple-tooltip-w-jquery-css/
http://www.sohtanaka.com/web-design/examples/element-tooltip/