.div_screen {
            top: 1%;
            left: 1%;
            height: 100%;
            width: 100%;
            position: absolute;
            object-fit: fill;
            z-index: 1;
            background-size: 100% 100%;
            background-image: url("../im/class.png");
        }
 .but {
           
            position: absolute;
            width:20%;
            height: 10%;
            background-color: yellow;
            color: darkblue;
            font-family: David;
            font-weight: bold;
            font-size: 25px;
            z-index: 100;
        }
      .ok
        {
             position: absolute;
            background-color:darkorchid;
            width:100%;
            left: 0%;
            height:8%;
            top:92%;
        }
 .flip {
            background-color: lime;
        }