magento2 – Magento 2 How to add custom CSS to HTML Template?

I have a custom html template where I have classes.

On layout I have added my css like this:

<?xml version="1.0"?>
<page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd">
    <head>
        <css src="https://magento.stackexchange.com/css/application.css" />
    </head>
    <body> 
        <referenceContainer name="content">
            <block class="VendorApplicationBlockMain" name="application_send" template="Vendor_Application::application.phtml"/>
        </referenceContainer>    
    </body>
</page>

And inside PHTML i’m using a javascript component in order to render html template

Just like this:

 <div id="port-form" data-bind="scope:'port-form'">
      <!-- ko template: getTemplate() --><!-- /ko -->
      <!-- ko template: template2--><!-- /ko -->
      <!-- ko template: template3 --><!-- /ko -->
        <script type="text/x-magento-init">
        {
            "#port-form": {
                "Magento_Ui/js/core/app": {
                  "components": {
                        "port-form": {
                            "component": "Vendor_Application/js/port-app-form",
                            "quote_data": <?= /* @escapeNotVerified */ $data ?>,
                            "quantities": <?= /* @escapeNotVerified */ $quantities ?>
                        }
                    }
                }
            }
        }
        </script>

It’s not taking any effect

I get this error:

Refused to apply style from '.../en_US/css/application.css' because its MIME type ('text/plain') is not a supported stylesheet MIME type, and strict MIME checking is enabled

Greetings