html,
body {
    overflow-y: auto !important;
    /* optional, if horizontal scroll isn't needed: overflow-x: hidden; */
}

.wap-frontend .wap-button-style-preset__preview-btn {
    position: fixed;
    width: 50px !important;
    height: 50px !important;
    bottom: 100px !important;
    right: 27px !important;
}