안녕하세요 하루에 3분                      #t {width:100px; height:100px; background:RGBA(0,0,0,0.3); border:3px solid black; position:absolute; left:50px; top:50px;}             #c {}             .c {width:100px; height:100px; background:yellow; border-radius: 30px; border:3px dotted black; z-index:-1;}}                                                                             //document.getElementById("c").style.display = "none";             var elem = document.getElementsByClassName("c");             for(var i = 0; i < elem.length; i++){                 elem[i].style.display = "none";             }