Editing buy now button

Hi,

I’m wondering could I change the button to a picture? If not, how do I center the button and get rid of the grey “shadow” or box around it?

Now it looks like this in CSS box:

.wc_quick_buy_btn {
background-color: #01a277;
width: 600px;
height: 100px;
font-size: 30px;
color: white;
}

Thank you!

https://www.ads-software.com/plugins/woocommerce-quick-buy/