AngleSharp by Florian Rappl

<PackageReference Include="AngleSharp" Version="0.2.6" />

 CSSNamespaceRule

public sealed class CSSNamespaceRule : CSSRule
Represents an @namespace rule.
namespace AngleSharp.DOM.Css { public sealed class CSSNamespaceRule : CSSRule { internal const string RuleName = "namespace"; private string _namespaceURI; private string _prefix; public string NamespaceURI { get { return _namespaceURI; } internal set { _namespaceURI = value; } } public string Prefix { get { return _prefix; } internal set { _prefix = value; } } internal CSSNamespaceRule() { _type = CssRule.Namespace; } } }