.fa-envelope-open:before {content:url('../fonts/extension/envelope-open.png');}
.fa-envelope-open-o:before {content:url('../fonts/extension/envelope-open-o.png');}
.fa-envelope-blue:before {content:url('../fonts/extension/envelope-blue.svg');}
.fa-envelope-blue-open:before {content:url('../fonts/extension/envelope-blue-open.svg');}