html {
    scroll-behavior: smooth;
    font-family: Helvetica, sans-serif, Arial;
}

body {
    margin: 0 auto;
    background-color: #222;
}

iframe {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: none;
    z-index: -1; /* Ensure the iframe stays behind other content */
    visibility: hidden; /* Initially hide the iframe */
    opacity: 0; /* Initially set opacity to 0 */
    transition: opacity 0.5s ease; /* Add a transition effect */
}
iframe.visible {
    visibility: visible;
    opacity: 1;
}