Unable to centre align button text

Thanks for the plugin. I am finding one issue with it, I am unable to centre align button text. There are not setting in the backend other than to change color so I am trying it with CSS, I removed the mail image png with css, but still unable to centre align the text. Hope you can help me solve this issue as soon as possible. Please give me the CSS code for changing the mail png and to centre align the text.

TIA