gentelella/vendors/datatables.net-fixedheader-bs/css/fixedHeader.bootstrap.css

Gentelella Admin is a free to use Bootstrap admin template

table.dataTable.fixedHeader-floating,
table.dataTable.fixedHeader-locked {
  background-color: white;
  margin-top: 0 !important;
  margin-bottom: 0 !important;
}

table.dataTable.fixedHeader-floating {
  position: fixed !important;
}

table.dataTable.fixedHeader-locked {
  position: absolute !important;
}

@media print {
  table.fixedHeader-floating {
    display: none;
  }
}