How to Apply CSS on HTML to Excel export

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>

via Chebli Mohamed