Hello,
01. you select the quantity and then click on the add to cart button. The background of quantity will be removed. It is the default functionality of the theme. it is present in all the demo.
02. Please add this code to the Theme Settings > Custom CSS > Global:
input.minus {
border-top-left-radius: 20px !important;
border-bottom-left-radius: 20px !important;
}
input.plus {
border-top-right-radius: 20px !important;
border-bottom-right-radius: 20px !important;
}
Best Regards.