custom services icon

This question was asked here https://colorlibsupport.com/t/change-service-icons/

The response was Please go to Appearance > Customize > Additional CSS and add the following code:

/Service icon replacement/
.service-icon {
content: url(http://placehold.it/350×150);
}

Which I have done however the image is not centered (it sits to the left). How do I ensure it is centered in all browsers like the previous icon was?