This theme supports rendering beautiful math in inline and display modes using MathJax 3 engine. You just need to surround your math expression with 

1

$$
, like 
1

$$ E = mc^2 $$
. If you leave it inside a paragraph, it will produce an inline expression, just like \(E = mc^2\).

To use display mode, again surround your expression with 

1

$$
and place it as a separate paragraph. Here is an example:

\[\sum_{k=1}^\infty |\langle x, e_k \rangle|^2 \leq \|x\|^2\]

You can also use 

1

\begin{equation}...\end{equation}
instead of 
1

$$
for display mode math. MathJax will automatically number equations:

\begin{equation} \label{eq:cauchy-schwarz} \left( \sum_{k=1}^n a_k b_k \right)^2 \leq \left( \sum_{k=1}^n a_k^2 \right) \left( \sum_{k=1}^n b_k^2 \right) \end{equation}

and by adding 

1

\label{...}
inside the equation environment, we can now refer to the equation using 
1

\eqref
.

Note that MathJax 3 is a major re-write of MathJax that brought a significant improvement to the loading and rendering speed, which is now on par with KaTeX.