How to change the width of the quantity field.

How to change the width of the quantity field. Today it's 2 digits, but I need min 3 digits, cause sometimes customers will consume 210 botles of Cola Zero... 

How to change this? 

Using custom CSS codes that you can inject to your form, you can change the width of the Quantity field of each product on the payment field.

Here's the code that you will need to inject.

.form-textbox.form-product-custom_quantity {

    width: 100px !important;

}

Reference Guide: How-to-Inject-Custom-CSS-Codes