system/HTTP/ContentSecurityPolicy.php
public function addStyleSrc($uri, ?bool $explicitReporting = null)
	{
		$this->addOption($uri, 'styleSrc', $explicitReporting ?? $this->reportOnly);

		return $this;
	}
public function addStyleSrc($uri, ?bool $explicitReporting = null)
	{
		$this->addOption($uri, 'styleSrc', $explicitReporting ?? $this->reportOnly);

		return $this;
	}
Adds a new valid endpoint for CSS file sources. Can be either
a URI class or a simple string.

@see http://www.w3.org/TR/CSP/#directive-connect-src

@param string|array $uri
@param boolean|null $explicitReporting

@return $this