How to use custom colour for button in Store "Purchase" and Header button?

Hello,

I would like to ask you for advice how could I update the colour of the Purchase and Header buttons across my web site? 
Is it possible to use custom colour which is different from what is specified in colour pallet for my website?

The button within Header is changing colour based on background (I guess). Is it possible to define both colours? 

Thank you very much for your time to help me. 🙂

Web Site URL: https://www.slovakspots.com/shop/p/gas-station-i
Password: Ulicajekrasnydom

@abibacon Thank you very much! 
I would like to ask one additional quick question, what is the selector for this Purchase button? 🙂 

Hey @GregOvens, you should be able to use the below

.products .sqs-add-to-cart-button {


}

@abibacon Thank you so much! 🙂