How to Apply CSS on HTML to Excel export - php

Question

I am trying to export HTML to Excel format using php headers, but CSS styling is not applying on elements (while export to excel file), I also try to implement Bootstrap Classes, but no luck
Note: while applying bootstrap classes, I included the bootstrap.css in my html
Is there any way available to apply CSS?
Headers using
header('Content-type: application/excel');
header("Content-Disposition: attachment; filename=\"$filename\"");
Sample HTML elements
<table width="100%" border="1" class="table table-striped table-bordered">
<thead>
<tr>
<td colspan="9" style="font-weight: bold; font-size: 16px; text-align: center;"><h2>Push Notification </h2></td>
</tr>
<tr><td colspan="9"></td></tr>
</thead>
<tbody>
<tr class="heading">
<th colspan="2" ></th>
<th style="width:2% !important">S.no</th>
<th style="width:10% !important">Date</th>
<th style="width:10% !important">App</th>
<th style="width:20%">Category</th>
<th colspan="2" style="width:50%">Message</th>
</tr>
#if($push_notifications->count() > 0)
<?php $counter = 1; ?>
#foreach($push_notifications as $notification)
<tr #if(($counter %2) ==1) bcolor="#c9c9c9" #endif>
<td colspan="2"></td>
<td style="width:2% !important">{!!$counter!!}</td>
<td style="width:10% !important">{!!$notification->date!!}</td>
<td style="width:10% !important">{!!$notification->notificationAppType->name!!}</td>
<td style="width:20%">{!!$notification->notificationCategory->name!!}</td>
<td colspan="2" style="width:50%">{!!htmlentities($notification->message, ENT_QUOTES)!!}</td>
</tr>
<?php $counter++; ?>
#endforeach
#else
<tr>
<td colspan="9">No record available</td>
</tr>
#endif
</tbody>
</table>

Answer 1

Short answer is no, you can't apply css to excel.
You can, however, apply some formatting to the text of excel files, but the amount of formatting is limited by the library you use to generate the excel file and to what formatting the excel itself permits.