The optional pseudo-class for CSS applies when an element is optional.
selector:optional { property: value; }
required
active
any-link
autofill
blank
checked
default
defined
dir
disabled
empty
enabled
first-child
first-of-type
focus
focus-visible
focus-within
fullscreen
has
hover
in-range
indeterminate
invalid
is
lang
last-child
last-of-type
link
local-link
modal
not
nth-child
nth-col
nth-last-child
nth-last-col
nth-last-of-type
nth-of-type
only-child
only-of-type
out-of-range
picture-in-picture
placeholder-shown
popover-open
read-only
read-write
root
scope
target
valid
visited
where
World Wide Web Consortium (W3C)