The only CSS present is the user-agent stylesheets defined by your browser.
Why do this? #
Removing CSS reveals the content hierarchy embedded within the HTML.
Good HTML, known as semantic HTML is very important for accessibility. Picking the appropriate HTML element for a given piece of content goes a long way for assistive technologies such as screen readers.
Screen readers aren't the only beneficiaries. If our CSS fails to load all users will appreciate our deliberate selection of HTML. Non-human users such as web crawlers and RSS readers will also have an easier time digesting our content.
In short: Semantic HTML surfaces the most important content, whilst facilitating progressive enhancement.