Using pixel sizing

This paragraph uses a size 12px font. This fails basic WCAG requirements for being too small. Additionally, it cannot be changed by the user via browser font-size settings.

While this paragraph uses a size 16px font (as recommended in WCAG), because it uses pixel sizing it will override the users' font settings.

This paragraph uses a 20px font size. While larger font sizes can be useful and improve readability, it is better to leave this to users to decide for themselves.

Using rem sizing

This paragraph uses a 0.9rem font size, which makes it a little smaller than the default browser fontsize. It's usually not a good idea to go below the default fontsize.

While this paragraph uses a 1rem font size, meaning it is set to the default browser fontsize.

This paragraph uses a 1.5rem fontsize. Larger fonts can be used to highlight short snippets of text (like in headings, pull quotes, etc.).