I am trying to edit my theme in Magento 2. I am using the Theme “Fastest”, and I am trying to do things such as add background images. I am looking for an HTML file for editing the header and body of the pages. I have tried looking for a .phtml file in my theme directory, but all I have been able to find are .xml files. I am wondering if there is an HTML file to create page content in Magento 2 or if this is exclusively done by XML files.