lab6.css

        body {
            font-family: Arial, Helvetica, sans-serif;
            font-size: medium;
        }
        
        .sticky {
          position: sticky;
          top: 0;
          z-index: -1;
        }

        #watermark{
            width: 100%;
            height: 500px;
        }

        #ad{
            display: none;
        }

        #myBtn{
            padding: 16px 64px;
            font-size: medium;
        }

        .modal {
            display: none;
            position: fixed; 
            z-index: 1; 
            padding-top: 100px; 
            left: 0;
            top: 0;
            width: 100%; 
            height: 100%; 
            overflow: auto; 
            background-color: rgb(0,0,0); 
            background-color: rgba(0,0,0,0.4); 
        }

        .modal-content {
            background-color: #fefefe;
            margin: auto;
            padding: 20px;
            border: 1px solid #888;
            width: 50%;
        }

        .close {
            color: #aaaaaa;
            float: right;
            font-size: 28px;
            font-weight: bold;
        }

        .close:hover,
        .close:focus {
            color: #000;
            text-decoration: none;
            cursor: pointer;
        }