Hello,
1) Don’t see problems with the – or + anymore https://gyazo.com/ed3f7d5feb6dd5b4c407a4235afcf696
Do you have this issue for all the products or for some products only? Could you, please, provide us with link to product with issue? What browser do you use?
2) Add the following code to Theme Options > Custom CSS to increase the buttons for the mobile devices
@media screen and (max-width:768px){
div.quantity > span, td.quantity > span {
width: 35px;
}
}
Regards