This table lists all CSS selectors and whether they are supported.

Selector	Example	Supported	Notes
Simple Selectors
Type	*input	YES
Class	.classname	YES
ID	#id	YES
Universal	*	YES
Attribute	a[attr~=value]	YES
Combinators
Adjacent sibling	img + p	CONDITIONAL*	EnableComplexCSSSelectorsStyling must be set to true
General sibling	p ~ span	CONDITIONAL*	EnableComplexCSSSelectorsStyling must be set to true
Child	div > span	CONDITIONAL*	EnableComplexCSSSelectorsStyling must be set to true
Descendant	li li	CONDITIONAL*	EnableComplexCSSSelectorsStyling must be set to true
Pseudo classes
active	p:active	YES
any	matches(header, main)
any - link	a:any-link
checked	input:checked
default	input:default
defined	simple-custom:defined
dir()	:dir(rtl)
disabled	input:disabled
empty	p:empty
enabled	input:enabled
first	@page :first
first - child	p:first-child	YES**
first - of - type	p:first-of-type
fullscreen	div:fullscreen
focus	input:focus	YES
host	:host
host()	:host(.special-custom-element)
host - context()	:host-context(h1)
hover	p:hover	YES
indeterminate	input:indeterminate
in - range	input:in-range
invalid	form:invalid
lang()	p:lang(en)
last - child	p:last-child	YES**
last - of - type	h2:last-of-type
left	@page :left
link	a:link
not()	:not(p,h1)
nth - child()	:nth-child(4n)	PARTIAL**	No support for the `[ of <complex-selector-list> ]` syntax.
nth - last - child()	:nth-last-child(4n)
nth - last - of - type()	p:nth-last-of-type(4n)
nth - of - type()	p:nth-of-type(4n)
only - child	h2:only-child	YES**
only - of - type	p:only-of-type
optional	input:optional
out - of - range	input:out-of-range
read - only	input:read-only
read - write	input:read-write
required	input:required
right	@page :right
root	:root	YES
scope	:scope
target	:target
valid	input:valid
visited	a:visited
Pseudo elements
after	a::after	YES
before	q::before	YES
cue	::cue
first - letter	p::first-letter
first - line	p::first-line
selection	::selection	PARTIAL	only color and background-color properties
slotted	::slotted(span)

To use these selectors you must set EnableComplexCSSSelectorsStyling to true either through the C++ parameter value or via the –enable-complex-css 1 command line argument when using the Player. You can switch them on or off. Disabling them increases performance.*

** Structural pseudo-class selectors cause additional style rematching of direct children in the DOM tree which affects performance. They should be used only when necessary.