required

The required CSS pseudo-class applies when an element is required.

selector:required
{
    property: value;
}

optional

active

any-link

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

optional

out-of-range

picture-in-picture

placeholder-shown

read-only

read-write

root

scope

target

valid

visited

where

World Wide Web Consortium (W3C)