Fonts
The following guidelines will improve the readability of your Web pages and allow your users to effortlessly read and scan through your content. Please note that persons with visual impairments will set their Web browser or other assistive technology software to display text larger than was intended by a Web page author. For this reason, it is important to use fonts and font sizes that allow Web users to scale the text. Cascading Style Sheets (CSS) help control the consistency of typography for a Web page, and makes it easier to implement scalable fonts across a site. Please see the CSS section for more information on using CSS to control font sizes.
Use Scalable font size
In order for a site to be more accessible to Web users, fonts should not be a 'fixed' point size. When choosing a font size for text, it is recommended fonts be sized using percentages (%) or ems. These font values are scalable on a Web page for users with poor vision. This gives them the ability to increase the font size if necessary.
Use Common Font Types
Common fonts used on the web such as Times Roman, Georgia serif (serif fonts) and Arial, Helvetica, and Verdana (sans-serif fonts) improve reading speed and are more likely to be consistent across multiple platforms and browsers. However, it is important to test your fonts on both Macintosh and Windows based computers (at a minimum) because they use different common fonts.
Use Dark Text On Light Backgrounds And Avoid Background Textures
Research shows that dark text on a light background maximizes contrast, improves readability, and reduces eyestrain. It is recommended that Web sites should use either black or dark gray text on a slightly off-white background (e.g. use color code of #FEFEFE). The use of a background pattern behind text can reduce this contrast and should be avoided.
Draw Attention To Your Text With White Space
User's eyes are attracted to strong contrast and distinctive patterns within your Web page. Therefore, you should help users focus on the text by separating it from other elements on the page with white (blank) space.
Avoid All Uppercase Letters In Headings
Uppercase headings form rectangular blocks of text that make it difficult for users to identify letters and words. It is recommended that you use title case headings consistently (capitalize the first letter of each word) throughout your site.
Fonts Appear Smaller On Macintosh Computers
The Macintosh operating system will display fonts approximately one size (2-3 points) smaller than the same fonts on a Windows operating system. This can have a dramatic impact on the readability of your site, so be sure to test your design on both platforms.
Cascading Style Sheets Help Maintain Consistency In Font Usage
For more information see the CSS (Cascading Style Sheets) section