The HTTP Content-Security-Policy (CSP) style-src-elem directive specifies valid sources for stylesheet <style> elements and <link> elements with rel="stylesheet".

The directive does not set valid sources for inline style attributes; these are set using style-src-attr (and valid sources for all styles may be set with style-src).

Syntax

Content-Security-Policy: style-src-elem 'none';
Content-Security-Policy: style-src-elem <source-expression-list>;

This directive may have one of the following values:

'none'

No resources of this type may be loaded. The single quotes are mandatory.

<source-expression-list>

A space-separated list of source expression values. Resources of this type may be loaded if they match any of the given source expressions. For this directive, the same source expression values are applicable as for style-src, with the exception of 'unsafe-hashes'.

style-src-elem can be used in conjunction with style-src:

Content-Security-Policy: style-src <source>;
Content-Security-Policy: style-src-elem <source>;

Examples

Violation cases

Given this CSP header:

Content-Security-Policy: style-src-elem https://example.com/

…the following stylesheets are blocked and won't load:

<link href="https://not-example.com/styles/main.css" rel="stylesheet" />

<style>
  #inline-style {
    background: red;
  }
</style>

<style>
  @import "https://not-example.com/styles/print.css" print;
</style>

…as well as styles loaded using the Link header:

Link: <https://not-example.com/styles/stylesheet.css>;rel=stylesheet

Specifications

Browser compatibility

See also

• Content-Security-Policy
• style-src
• style-src-attr
• Link header
• <style>, <link>
• @import
• CSSStyleSheet.insertRule()
• CSSGroupingRule.insertRule()
• CSSStyleDeclaration.cssText