Setting Button Image caption in the middle!

Through CSS i am able to get the v.nativebutton looking the way i want to, but i can’t get the caption to be right in the middle of my icon/image. Attached is the screen shot of what the button looks like when i add text -align: center to my CSS style sheet. Any idea on how i can set the caption of the button to be right in the middle of my icon image?
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