#overlay{
            position: fixed;
            top:0;
            z-index: 10;
            width: 100vw;
            height: 100vh;
            visibility: hidden;
            opacity: 0;
            background: rgba(0,0,0,0.6);
            transition: all 0.5s ease-out;
        }
        #overlay.overlay_on{
            visibility: visible;
            opacity: 1;
        }

        .flex{
            width: 100%;
            height:100%;
            display: flex;
            justify-content: left;
            align-items: center; 
        }
        #overlay_inner{
            padding:10px 60px;
            background-color:#FFF;
            text-align:center;
        }

        #close_btn{
            display:block;
            margin:20px auto;
            padding:10px 30px;
            background-color:#eee;
            border:solid #ccc 1px;
            cursor: pointer;
        }

        #open_btn{
            display:inline_block;
            margin:20px auto;
            cursor: pointer;
        }