Although EchoSVG supports level 4 selectors, the rest of CSS is only supported at CSS 2. Current SVG images tend to use modern CSS, for example:

• Custom properties (see Render MermaidJS diagrams #35).
• Level 4 values and units (including calc() and other functions).
• Media queries.

This issue is opened to discuss the transition of this project to a more modern CSS. The intention is to migrate the current CSS Object Model to something based on CSS4J's Object Model.