You can select the component as a class and modify it however you wish. Advanced changes will have to be modified by injecting the style tag into the component. See:

How do I inject into the Shadow DOM into the PERC components?

NFT Buy Button - NFT product redemption

<style>
nft-buy-button {
  color: black;
}
</style>
<nft-buy-button product="{{product.id}}" >Buy with NFTs</nft-buy-button>

NFT Token Gate

<style>
nft-connect {
  color: black;
}
</style>
<nft-connect product="{{product.id}}" variant="{{product.variants[0].id}}" />