docs: editorial fixes (#6889)

website/docs/guides/markdown-features/markdown-features-math-equations.mdx

@@ -17,9 +17,10 @@ Please read [KaTeX](https://katex.org) documentation for more details.
 
 Write inline math equations by wrapping LaTeX equations between `$`:
 
-```mdx
-Let $f\colon[a,b] \to \R$ be Riemann integrable. Let $F\colon[a,b]\to\R$ be $F(x)=
-\int_{a}^{x} f(t)\,dt$. Then $$F$$ is continuous, and at all $x$ such that $f$ is continuous at $x$, $F$ is differentiable at $x$ with $F'(x)=f(x)$.
+```latex
+Let $f\colon[a,b]\to\R$ be Riemann integrable. Let $F\colon[a,b]\to\R$ be
+$F(x)=\int_{a}^{x} f(t)\,dt$. Then $F$ is continuous, and at all $x$ such that
+$f$ is continuous at $x$, $F$ is differentiable at $x$ with $F'(x)=f(x)$.
 ```
 
 <BrowserWindow>
@@ -33,7 +34,7 @@ Let $f\colon[a,b] \to \R$ be Riemann integrable. Let $F\colon[a,b]\to\R$ be $F(x
 
 For equation block or display mode, use line breaks and `$$`:
 
-```mdx
+```latex
 $$
 I = \int_0^{2\pi} \sin(x)\,dx
 $$