Since the beginning of the Facebook, there was only the Share button for publishers. After that, Facebook in 2010 introduced the new like and share buttons with a different integration options and fast loading.
Yesterday in a blog post, Facebook announced that they are rolling out the new design for the Like and Share buttons. The new buttons are designed in such a way to increase the engagement among users and to ultimately increase the referral traffic. The buttons have already rolled out in some places and will be rolled out to everyone in the coming weeks.
The publishers who are currently using the old Like and Share buttons will automatically upgraded to the new buttons as soon as the new design rolls out in their region. So, you don't need to add any new code to your site.
Talking about the design of new buttons, the layout is pretty much the same as you can see in the image. The border radius is increased on the Like and Share links. The old buttons had blue and sky blue color scheme, but now white and blue is the new color scheme and looks like the default font is also changed.
The thumbs up icon is also changed and now has grey color. You will be able to customize the buttons just like the current buttons, as soon as they arrive for you. The Send button with the Like button is now replaced with Share button. The Send button will remain for backwards compatibility only.