Fasel/fasel-jfx/src/main/resources/css/send_button.css

.toggle-button {
  -fx-graphic: url('/img/icons/baseline_send_black_18dp.png');
  -fx-effect: null;
  -fx-background-color: transparent;
}

.toggle-button:selected {
  -fx-graphic: url('/img/icons/baseline_send_black_18dp.png');
  -fx-effect: null;
  -fx-background-color: transparent;
}