@media screen and (max-width: 980px) {
    /* 1. Force the main container to behave as a column */
    /* Indico legacy often uses a fixed-width container (.conf) */
    .conf, #main-container, .conference-page-container {
        width: 100% !important;
        display: block !important;
    }

    /* 2. Target the side menu container you identified */
    .conf_leftMenu {
        width: 100% !important;
        float: none !important;
        margin-bottom: 20px !important;
        padding: 0 10px !important;
        box-sizing: border-box;
    }

    /* 4. Force the main content area to full width */
    /* Usually follows the menu; might be a div or a td depending on the exact version */
    .conf_leftMenu + div, 
    .conf_rightContent, 
    .conference-page-content {
        width: 100% !important;
        margin-left: 0 !important;
        float: none !important;
        display: block !important;
    }
}