function displayHideUI()
{
     var ui = document.getElementById("bbs");
     ui.style.display="none";
}
function displayShowUI()
{
     var ui = document.getElementById("bbs");
     ui.style.display=" ";//display為空的話會好使，為block會使后邊的空間換行
}
function visibilityHideUI()
{
     var ui = document.getElementById("bbs");
     ui.style.visibility="hidden";
}
function visibilityShowUI()
{
     var ui = document.getElementById("bbs");
     ui.style.visibility="visible";
}
</script>