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  $$...$$ 
instead of  1   for display mode math. MathJax will automatically number equations:

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

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