How to change the background of table head in print format?

I am unable to change the background of table head.
Can anyone suggest how to make the background of table head white?

I have tried the following style but doesn’t seem working.

> <style>
> .hg-table > thead > tr > th,
> .hg-table > tbody > tr > th,
> .hg-table > tfoot > tr > th,
> .hg-table > thead > tr > td,
> .hg-table > tbody > tr > td,
> .hg-table > tfoot > tr > td {
>   padding: 8px;
>   line-height: 1.42857143;
>   vertical-align: top;
>   border:0.1em dotted #000000; 
>   background-color:#ffffff; 
>   border-top: 0.1em dotted #000000;
> }
> </style>
> <table class="hg-table">
>       <thead>
>         <tr>
>             <th class = "text-left">Sr</th>
>             <th class="text-left">ITEM CODE</th>
>             <th class="text-left">PART NO.</th>
>             <th class = "text-left">DESCRIPTION</th>
>             <th class = "text-left">QTY.</th>
>             <th class = "text-left">UNIT PRICE</th>
>            <th class = "text-left"> AMOUNT</th>
>         </tr>
>      </thead>

Override these classes

.print-format th {
  background-color: //your color
}

it is not working.

Still same result
> .hg-table > thead > tr > th,
> .hg-table > tbody > tr > th,
> .hg-table > tfoot > tr > th,
> .hg-table > thead > tr > td,
> .hg-table > tbody > tr > td,
> .hg-table > tfoot > tr > td {
> padding: 8px;
> line-height: 1.42857143;
> vertical-align: top;
> border:0.1em dotted #000000;
> background-color:#ffffff;
> border-top: 0.1em dotted #000000;
> }
> .print-format th{
> background-color:#ff0000;
> }

> <table class="hg-table">
>   <thead>
>     <tr>
>         <th class = "text-left">Sr</th>
>         <th class="text-left">ITEM CODE</th>
>         <th class="text-left">PART NO.</th>
>         <th class = "text-left">DESCRIPTION</th>
>         <th class = "text-left">QTY.</th>
>         <th class = "text-left">UNIT PRICE</th>
>        <th class = "text-left"> AMOUNT</th>
>     </tr>
>  </thead>

Try adding !important to the style.