What button are you referring to? Based on your previous thread, you're using the Share plugin. So, you can use any image you want as an input trigger.
This is now independent thread as I am referring to Twitter plugin. I am aware that I can do that with share plugin. To explain little bit more I have concluded that share plugin is better for mobile, while Twitter and Facebook plugins are better for PC. Now problem is that Twitter plugin doesn't allow me to change its look neither to call its functions. Thank you.