This one is pretty simple and, although I'm sure it'll be updated in a future release, I figured there might be others who would like to go ahead and get this updated now. Also, I'm not sure if it's been shared before but, if it has, I couldn't find it so here goes...
First thing you'll want to do is add the following code to your extra.less template.
CSS:
.shareButtons-button.shareButtons-button--twitter:hover {
background-color: #000000;
}
.shareButtons--iconic...