How to toggle a <hr> tag in code behind(.aspx.cs page)?

Hi All,
i have a gridView and have the following requirements:
<hr> is hidden when first loading the page;
when there is data in gridView---> display <hr>;
if there is no data in gridView---> hide <hr>;

i am using javascript to do it but i found <hr> is always hidden, can anyone point me to the right direction?

attached the code.

<hr id="hrExport" style=" display:none;" />

*********************************
string javaScript = string.Empty; 

        
        if (dt.Rows.Count > 0)
        {

            javaScript = @"<script type='text/javascript' >
                                function DisplayHr1() {
                                    var hr = document.getElementById('hrExport');
                                    hr.style.display = 'block'; 

                                }</script>";
            Page.ClientScript.RegisterStartupScript(this.GetType(), "DisplayHr1", javaScript); 


        }
        else
        {
            javaScript = @"<script type='text/javascript' >
                                function DisplayHr2() {
                                    var hr = document.getElementById('hrExport');
                                    hr.style.display = 'none'; 

                                }</script>";
            Page.ClientScript.RegisterStartupScript(this.GetType(), "DisplayHr2", javaScript); 

        }

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