However, I would strongly recommend that you do NOT change the standard MathJax delimiters( \( ... \), \[ ... \] ), as described in the FAQ above.
As for changing the font size and color only for the MathJax block within a specific class, I think you can do it using CSS as you did in version 2.x. But, the HTML tags and classes used by MathJax are different between 3.x and 2.x. You can use Google Chrome to inspect the webview of the card screen so you can see what tags and classes MathJax uses.
Thank you for your reply. I tried inspecting the webview but I literally don’t know what to look for. Is there anyone who could help me, or has anyone already extracted the new Mathjax HTML tags and classes?