jquery 让div居中显示

function showsearch(){ var wnd = $(window), doc = $(document);  var left = doc.scrollLeft();  var top = doc.scrollTop(); left += (wnd.width() - $("#seachdiv").width())/2;  top += (wnd.height() - $("#seachdiv").height())/2;   $("#seachdiv").css("position","absolute");  $("#seachdiv").css("top",top);  $("#seachdiv").css("left",left); if($("#seachdiv").css("display")=="none") { $("#seachdiv").show("slow"); }else { $("#seachdiv").hide("slow"); }}