DefaultList columns header is half hidden in fluentui

I am using fluentui for creating the webapp. I used DefaultList component to show the list of data.

But the header of all the columns is half hidden like below

All the rows below are being visible correctly.

This is the code snippet I am using

<DetailsList
        items={operations}
        columns={columns}
    checkboxVisibility={2}
    setKey="set"
    selectionMode={SelectionMode.none}
    onRenderItemColumn={_renderItemColumn}
/>