/* Hide everything inside the MessageBar (icon, text, buttons) */
#CardGallery-CardGallery-pcf-container-id .fui-MessageBar * {
    display: none !important;
}

/* Hide the raw text node by setting font-size to 0 */
#CardGallery-CardGallery-pcf-container-id .fui-MessageBar {
    font-size: 0 !important;
}

/* Insert your custom message */
#CardGallery-CardGallery-pcf-container-id .fui-MessageBar::after {
    content: "No events are currently open for registration.";
    display: block;
    font-size: 16px !important; /* restore readable size */
    color: #444;
    text-align: center;
    padding: 20px;
}