Moving category header to main content

Create a custom Argento theme
Create/add Magento_Catalog/layout/catalog_category_view.xml in your custom theme

Add following content to it:

<?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">
    <body>
        <move element="page.main.title" destination="content.top" before="-" />
        <move element="category.view.container" destination="content.top" after="page.main.title" />
    </body>
</page>

Flush the store cache