how to change button style in datatable code example

Example: button style in jquery datatable

$(document).ready(function() {
    $('#example').DataTable( {
        dom: 'Bfrtip',
        buttons: [
            {
                extend:    'copyHtml5',
                text:      '<i class="fa fa-files-o"></i>',
                titleAttr: 'Copy'
            },
            {
                extend:    'excelHtml5',
                text:      '<i class="fa fa-file-excel-o"></i>',
                titleAttr: 'Excel'
            },
            {
                extend:    'csvHtml5',
                text:      '<i class="fa fa-file-text-o"></i>',
                titleAttr: 'CSV'
            },
            {
                extend:    'pdfHtml5',
                text:      '<i class="fa fa-file-pdf-o"></i>',
                titleAttr: 'PDF'
            }
        ]
    } );
} );