That's because this website doesn't use any page-level style sheet. Most of the XHTML is also written by hand.
There are several reasons for this, and I would lie if I said that me being lazy wouldn't have played a role. However, the most important reason is that I wanted to make a statement, namely that I don't think that most modern websites are particularly well designed. They might be beautiful, but that's only a small part of a website's user experience. Other important parts of the UX are that the website's content can be navigated easily, that the information the viewer wants to see is easy to find and presented in a readable way, that there are no distractions from the content, that the website loads fast, that it can be accessed on a Braille terminal,… Those aspects are where too many modern websites are lacking.
The lack of (almost) all custom design, with a focus on the text content, is meant to contrast this sad trend.
Most browsers have settings that allow to customize colours and fonts used by websites without a style sheet. In Mozilla Firefox, for instance, you can find the settings for default colour and font in the "General" category in the browser's preferences, under "Language and Appearance".
A word of warning though: Many websites supply incomplete style sheets. They assume that the user's browser is configured to display black text on a white background and become unusable if one or both of these colors are changed.
An interesting feature most browsers offer is to intentionally ignore the style sheet supplied by a website. This can help to improve readability, if the style sheet of the site is particularly bad. Again, in Firefox, you can find the respective feature in the "View" menu (visible after pressing the ALT key). The entry is called "Page Style".