Magento 2 – How to Add Custom Div Before Main Content

You could try adding a new structural block and echo this out before the tag where you require.

<default>
    <reference name="root">
        <block type="core/text_list" name="my_before_body" as="my_before_body" translate="label">
            <label>My before body</label>
        </block>
    </reference>
    <reference name="my_before_body">
        <block type="core/template" name="marketplace_player" template="magenetwork/list.phtml">
    </reference>
</default>

You would then need to echo out this new structural block in your page templates before the body tag

<?php echo $this->getChildHtml('my_before_body') ?>

If you're interested, the answer is to use a referenceContainer in the XML file and add the new Class / ID names to the DIV / XML container.

For example:

<referenceContainer name="main.content" htmlTag="main" htmlId="add-ID-name-to-container" htmlClass="new-class-name"/>

The rendered DIV (main) will look like:

<main id="add-ID-name-to-container" class="new-class-name" >

    ...

</main>

The un-edited/updated version would look like:

<main id="maincontent" class="page-main" >

    ...

</main>