Show/hide widget per mobile/tablet/desktop

My first attempt has been unsuccessful.
I have added the following css class to my custom css wordpress plugin:

.hidden-everything { display: none; }

I have added the class to Widget CSS Classes (so I can now select it from the drop down box for each widget).

For one of my widgets in the footer I have selected the hidden-everything class and saved changes. I would expect now that the widget is not displayed at all (for all devices) but it IS still being displayed. Am I doing something wrong or is it that your plugin is simply not meant for this kind of thing?

http://ww.wp.xz.cn/plugins/widget-css-classes/