Responsive box

Hi,
The plugin is great. However I tried to use it also for mobile devices and add the code, which was mentioned in the FQA section, to my function.php, but it doesn’t work properly.
Please be so kind and infor me, how can I setup the width element of the box in %? For example width:30% would be fine fot the box and 100% for mobilephone…
Thank you evry much,
Andi

https://wordpress.org/plugins/scroll-triggered-boxes/