Thank you for tagging this task with good first task for Wikimedia newcomers!

Newcomers often may not be aware of things that may seem obvious to seasoned contributors, so please take a moment to reflect on how this task might look to somebody who has never contributed to Wikimedia projects.

A good first task is a self-contained, non-controversial task with a clear approach. It should be well-described with pointers to help a completely new contributor, for example it should clearly pointed to the codebase URL and provide clear steps to help a contributor get setup for success. We've included some guidelines at https://phabricator.wikimedia.org/tag/good_first_task/ !

Thank you for helping us drive new contributions to our projects <3

@NavinoEvans
I am currently exploring the MediaWiki codebase for the above task and need some assistance. I came across the following HTML snippet that appears to be part of a section header template:

html
<div class="mainpage_box">

<h3 data-mw-thread-id="h-Edit_and_use_MediaWiki-MediaWiki_is_a_collaboration_and_documentation_platform_brought_to_you_by_a_vibr">
    <span class="mw-headline" id="Edit_and_use_MediaWiki">
        <span data-mw-comment-start=""></span>
        <span class="header_icon" aria-hidden="true" role="presentation">
            <span class="mw-valign-middle" typeof="mw:File">
                <span>
                    <img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/8a/OOjs_UI_icon_edit-ltr.svg/20px-OOjs_UI_icon_edit-ltr.svg.png" decoding="async" width="20" height="20" class="mw-file-element" />
                </span>
            </span>
        </span>
        <span>Edit and use MediaWiki</span>
        <span data-mw-comment-end=""></span> 
    </span>
</h3>

</div>

Could you please guide me to the directory or file in the MediaWiki repository where this or similar templates are defined? Understanding this will greatly help in my preparation for contributing.