function getPos(obj){ var iTop = 0; while(obj){ iTop += obj.offsetTop; obj = obj.offsetParent; } return iTop; }
css 制作三角形
span{ border-top:10px dashed transparent; border-left:10px dashed transparent; border-right:10px dashed transparent; border-bottom:10px solid red; 0px; height: 0px; display: block; }