Why my datatable Fixed header doesn`t work /

I am trying to make my data table Thead a sticky one but when i tried fixed header than it doesn't work . I have tried position: fixed; , top: 0; and try to fix it with css but when a done this action than it works in firefox as expected but it doesn't work as expected in crome edge opera .

    "stateSave": false,
    "orderCellsTop": true,
    "fixedHeader": {
        header: true,
    },
    "columns": [
    {'data':'chk_select_header','orderable': false},

Here is my code of ajax .

from Why my datatable Fixed header doesn`t work /