How to remove the green box from a button click?

Hi

Just wanted to reach out and ask the group for help on removing an unwanted state appearance from a button I have created on my PDF CV.

Basically I have created a button inside my CV so that when you click on my email at the top, it automatically opens up the users default email programme and pops in my email address in the "To" field which is the expected behaviour , I have also customised the hover sate of the button to display a small red underline which is part of my branding, what I don't like however is that when you click the mouse down on the email link it creates a green box effect on the link itself, which I want to get rid of but not sure where or how I can remove this?

Any help would be much appreciated.

Link to my document can be found here:

https://drive.google.com/open?id=1Uqsc4Sw18xU6KFwDjSowu7qU8xzCOzT1

Dean