Can the look of the variant dropdown on the new shop update be changed?

Hi!
I am loving the new improvements to the shop to make it more e-commerce based. I have activated the "Add to Cart Feature" in the shop, but I don't love the look of the black border around the selection button. It just doesn't suit the aesthetic of my site.  

I used to have CSS for it when you clicked into the item and it had no top, left or right border, so it was just a line at the bottom and in my brand colour. (see image below)
I have tried fiddling with the CSS to restore this look but haven't saved it because it wasn't changing and I actually have no idea what I'm doing (lol). 
Any help would be so greatly appreciated! Thankyou! 🙂

My website: www.lumierechandlery.com.au 

How i would like to get it to look again:


What it currently is:

Hi,

Can you enable Variant? We can check easier

Thanks Tuanphan! Sorry for the delay i have been away. 
I have just reactivated the add to cart feature 🙂 thankyou for your help!

Hi Tuanphan,
That is perfect! I just hated that black box around the button but your code worked a charm! 
Cant thank you enough! These forums are really helpful. Thankyou 😄