Fullcalendar remove buttons borders/shadow

I try removing the Fullcalendar Buttons borders.

.fc-button { border: 0px !important; }

But when I click on it a new border appear :

And didn’t found which element display this border.

Note : On click the DOM not seems to change

>Solution :

I think that it comes from the box-shadow property that is added to the button thanks to the :focus pseudo-class.

You can try adding this rule :

.fc-button {
  box-shadow: none !important;
}