Text is not horizontally centered in button

Hello, the text in the buttons on my website is not centered and my novice attempts to add custom CSS to align have not been successful. In the attached image, you can see that the text is slightly misaligned to the left. 

I've tried 

button {
  text-align: center !important;
}

and variations of it.

Any ideas?

Thank you.

@CAB Can you share your site URL? 

For reference: https://www.atelierariana.com/team

Try this to Custom CSS box

div.button-block a {
    text-indent: 16px !important;
}

(16px is letter spacing, need to make sure letter spacing = text indent)