One of 1, 2, 3, 4, 5, or 6 specifying a font size, defaults
to NULL, in which case the argument is ignored. The sizes follow the
conventions of heading tags, so 1 is the largest font and 6 the
smallest.
weight
One of "light", "lighter", "normal", "bolder", or "bold" specifying the font
weight, defaults to NULL, in which case the argument is ignored.
If "bolder" or "lighter", the font weight is changed relative to the
current font weight.
style
One of "italic" or "normal" specifying the font
style, defaults to NULL, in which case the argument is ignored.
case
One of "upper", "lower", or "title" specifying the font case,
default to NULL, in which case the argument is ignored.
family
One of "sans-serif" or "monospace" specifying the font
family, defaults to NULL, in which case the argument is ignored.