\begin{dfn}\label{dfn:good} 

This is my definition of good.

\end{dfn}

\begin{thm}[Pythagorean theorem]\label{thm:pythagorean} 

For a right triangle, if \(c\) denotes the length of the hypotenuse and
\(a\) and \(b\) denote the lengths of the other two sides, we have

\end{thm}

\[a^2 + b^2 = c^2\]

\Cref{thm:pythagorean} is very popular and is unrelated to
\cref{dfn:good}.

And this is a normal definition list:

\begin{description}
\tightlist
\item[Day]
When the sun is above the horizon.
\item[Night]
When it is not day.
\end{description}