Go here and view the page for the line "Initial:". You will then find any initial values that spec specifies for rendering the text. However, for a font family, it indicates:
'font-family'
Value: [[ <family-name> |
<generic-family> ],]* [<family-name> |
<generic-family>] | inherit
Initial: depends on user agent
Applies to: text content elements
Inherited: yes
Percentages: N/A
Media: visual
Animatable: yes
This means that the user agent can decide which font family to use if none is specified, or if it cannot access the font with the given name.
: , CSS (, fill: red;). CSS .
, .