[Tutorial ] How to hide in mobile device

If you check using firebug or google chrome inspector each button has a parent element like this http://prntscr.com/c1ec82

copy the id and it should be something like fvfeedbackbutton907 where 907 is post id, for your site this value will be different

/* Landscape phone to portrait tablet */
@media (max-width: 767px) {
#fvfeedbackbutton907{
display: none;
}
}

/* Landscape phones and down */
@media (max-width: 480px) {
#fvfeedbackbutton907{
display: none;
}
}

Put this css code in your theme style sheet

https://ww.wp.xz.cn/plugins/wpfixedverticalfeedbackbutton/