If none of the font names defined in a font or font-family declaration are available on the browser of the user, the browser will display the text using its default font. It's recommended to always define a generic font family for each declaration of font or font-family to get a less degraded situation than relying on the default browser font. All browsers should implement a list of generic font matching these families: Serif, Sans-serif, cursive, fantasy, Monospace.

Noncompliant Code Example

a {
  font-family: Helvetica, Arial, Verdana, Tahoma; /* Noncompliant; there is no generic font family in the list */
}

Compliant Solution

a {
  font-family: Helvetica, Arial, Verdana, Tahoma, sans-serif;
}

See