Bare HTML With Custom Style In addition to extending/overwriting the default page layout template and CSS, as in the previous example, you can completely abandon the 'default' CSS of the site, and create a totaly independent one, that starts from a blank canvas. This requires the additional step of adding the layout of a page to 'barehtml' in the post's front matter, then you inherit nothing but the header metadata. All the content of your post is dropped directly into then page's body element. This means you can:

Sometimes you want to tweak the appearance of a particular page on your site, but don't want to have to create a whole new template, theme or layout. In those cases it's possible to use either Markdown, with some HTML, or a pure HTML, content file. This can be done by adding an additional css file into the page bundle folder, for your post, and adding it to a params.stylesheets variable, as shown below, which includes first the site’s usual CSS style sheet located at /css/style.css, and then the name of the style sheet added in the page bundle folder for the post. This order is very important.

This article offers a sample of basic Markdown syntax that can be used in Hugo content files, also it shows whether basic HTML elements are decorated with CSS in a Hugo theme.