How can I remove datatable button default class (btn-default)

anema

I am using Data table with Button. I want to show Success button rather default.
I tried this Code

buttons: [
{
extend: "excel",
className: "btn-sm btn-success",
titleAttr: 'Export in Excel',
text: 'Excel'
}]

This code is working but this is adding btn-success class, But I want first remove the btn-default class thn add the success class.

Current Classes: "btn btn-default buttons-excel buttons-html5 btn-sm btn-success"
What I want : "btn buttons-excel buttons-html5 btn-sm btn-success"