[Plugin: Social Sharing Toolkit] Edit CSS of Tumblr Button

First, sorry, my english is not good.

I have a CSS for all my image posts. I added the Facebook, Twitter, Pinterest and Tumblr buttons. But the Tumblr button get the CSS from my image posts.

I don’t want that, but I try to change it, but I can’t. I don’t find where I must change the code.

How I can change the CSS to remove de border?

My site: https://rufi.nosolowindows.com

Thanks.

https://www.ads-software.com/extend/plugins/social-sharing-toolkit/