CSSStyleSheet

CSS object model css-object-model

Baseline: Widely available on the web, in every major browser since Sep 2015, and long enough to count on (since Mar 2018).

niso: Partial 55%. 123 of 221 subtests pass, by system: Linux 55%, macOS 55%. Engines: QuickJS, the engine niso's WPT run uses; Node and Porffor have no recorded run. WPT results recorded at f3b4fa8, 2026-11-10; web-features 3.45.0. WPT tests · niso's support · CSS, CSSConditionRule, CSSGroupingRule, CSSMediaRule

CSSStyleSheet is an interface in idl/cssom.webidl, inheriting StyleSheet, exposed in Window. What it does is on MDN; this page says what niso has of it.

Status

The web features its members belong to, each with its Baseline status on the web and how much of the feature’s WPT suite passes in niso (see Web platform support).

Feature	On the web	In niso	Members
CSS object model	Widely available	Partial 55% 123 of 221 subtests pass	5

Members

ownerRule

attribute

readonly attribute CSSRule? ownerRule;

int32_t niso_css_style_sheet_get_owner_rule(niso_dom* dom, niso_handle self, niso_handle* out);

cssRules

attribute

[SameObject] readonly attribute CSSRuleList cssRules;

int32_t niso_css_style_sheet_get_css_rules(niso_dom* dom, niso_handle self, niso_handle* out);

insertRule()

operation

unsigned long insertRule(DOMString rule, optional unsigned long index = 0);

int32_t niso_css_style_sheet_insert_rule(niso_dom* dom, niso_handle self, const char* rule, size_t rule_len, uint32_t index, uint32_t* out);

deleteRule()

operation

undefined deleteRule(unsigned long index);

int32_t niso_css_style_sheet_delete_rule(niso_dom* dom, niso_handle self, uint32_t index);

rules

attribute

[SameObject] readonly attribute CSSRuleList rules;

int32_t niso_css_style_sheet_get_rules(niso_dom* dom, niso_handle self, niso_handle* out);

addRule()

operation

long addRule(optional DOMString selector = "undefined", optional DOMString style = "undefined", optional unsigned long index);

int32_t niso_css_style_sheet_add_rule(niso_dom* dom, niso_handle self, const char* selector, size_t selector_len, const char* style, size_t style_len, bool has_index, uint32_t index, int32_t* out);

removeRule()

operation

undefined removeRule(optional unsigned long index = 0);

int32_t niso_css_style_sheet_remove_rule(niso_dom* dom, niso_handle self, uint32_t index);

Not in niso yet

Members the web has, by the BCD keys web-features 3.45.0 lists, that idl/ doesn’t declare. The list is partial: web-features lists only the keys it maps to a feature.

• CSSStyleSheet (Constructed stylesheets)
• replace (Constructed stylesheets)
• replaceSync (Constructed stylesheets)