Font family is controlled by the font-family CSS attribute, like this h1 {font-family: Sans-serif;}
It allows you to pick a font to display to the user.
More font-family examples can be viewed at MDN
Note: Keep in mind that different computers and browsers will have different fonts enabled. Commonly available fonts are called Web Safe
p {
font-size: 16px;
font-family: Monospace;
}