You can apply the css from Appearance > Customize > Addditional css.
To clarify: Our plugin is designed to be as clean as possible out of the box without bells and whistles. Unfortunately your theme overrides some of the css of our plugin. This is something we can’t foresee for every theme out there. That’s why I provide you with some pointers to get it back to the way it’s designed by us.
If you want other fancy details; like the different color and size; that’s beyond the scope of our support.
We made it very easy to override the output by using template overrides by coping template files into YOUR_CHILD_THEME/woocommerce-auto-added-coupons/ in the same fashion as WooCommerce does this, but this requires some php/html/css knowledge.
I noticed one issue though; auto submitting isn’t working for the number-inputs that you use; I will provide a fix for this soon.