It is impossible to manipulate thead element. Only elements of th individually.
thead tr:first-child th {
position: sticky;
top: 0;
}
thead th {
position: sticky;
top: 20px;
background: khaki;
color: white;
}
<table class="table table-striped table-hover table-bordered text-center">
<thead>
<tr>
<th><input class="form-control" id="myInput" type="text" placeholder="Search.."></th>
<th><input class="form-control" id="myInput" type="text" placeholder="Search.."></th>
<th><input class="form-control" id="myInput" type="text" placeholder="Search.."></th>
<th><input class="form-control" id="myInput" type="text" placeholder="Search.."></th>
<th><input class="form-control" id="myInput" type="text" placeholder="Search.."></th>
<th><input class="form-control" id="myInput" type="text" placeholder="Search.."></th>
</tr>
<tr>
<th>gfdg</th>
<th>gdrgr</th>
<th>segsre</th>
<th>gfrdg</th>
<th>srgdr</th>
<th>egrsdg</th>
</tr>
</thead>
<tbody>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
<tr>
<td class="font-elephant">1</td>
<td class="font-elephant">7</td>
<td class="font-elephant">9</td>
<td class="font-elephant">585</td>
<td class="font-elephant">656</td>
<td>65654
</td>
</tr>
</tbody>
</table>
Or add the two tr into one.
<thead>
<tr>
<th>
<input class="form-control" id="myInput" type="text" placeholder="Search..">
<div>gfdg</div>
</th>
...
And then only this style is enough.
thead th {
position: sticky;
top: 0;
background: khaki;
color: white;
}