How to include custom theme directory CSS file into my CMS block?

[Aveeva]

I have created custom theme which is inherit from blank theme,

I have created more than one CMS block and include into CMS page for home page design.

One of my CMS block named service banner

In the CMS block i have created some design:

<div class=" container service-banner">

<div class="row">
<div> </div>
</div>

<div class="row">
<div> </div>
</div>

<div class="row">
<div> </div>
</div>

</div>

I have created _cms_block.less file under

app\design\frontend\Myrwd\mytheme\web\css\source\ _cms_block.less

@media only screen and (max-width: 600px) {
    .container service-banner{
        body {
            background-color: lightblue;
        }
    }
}

and imported into _extend.less file

@@import "_cms_block.less";

How to include custom theme directory CSS file into my CMS block?