Styling the Add To Cart & Choose Order Option

Hello,

It's possible, first have a look on this tutorial to see how to add some custom css command.

Second step, build a very specific custom css command, here the most important his the "target", in Css it's called the selector, see my pseudo code example :

Ex :
a.hikabtn.hikacart {
background- color: red;
}

Add your custom css code at the end of your css file, it's easier to find it later, and increase his priority.
If for a reason or another, you need to increase the priority, use an "!important"

Ex : background-color: red !important;

Hope this will help you to get what you need.
Regards