AngleSharp
The ultimate angle brackets parser library parsing HTML5, MathML, SVG
... with CSS. Therefore CSS is a first class citizen in the AngleSharp eco-system. Nevertheless, it is your choice if you want to use CSS with HTML, CSS alone or if you provide your own CSS solution. AngleSharp offers a lot of extension points. One of the best possibilities is providing scripting engines. This gives you a very elegant way of using JavaScript with C# on webpages. You can even script in other languages if you want to.