答案1
这种包装tcolorbox
非常适合做这种盒子。
\documentclass{article}
\usepackage{newpxtext}
\usepackage{newpxmath}
\usepackage{tcolorbox}
\tcbuselibrary{theorems}
\newtcbtheorem{theorem}{Theorem}{
arc=0mm,
fonttitle=\bfseries,
fontupper=\itshape,
coltitle=black,
colback=red!10,
colframe=red!10,
}{thm}
\begin{document}
\begin{theorem}{Fundamental Theorem of Algebra}{fundalg}
If
\[
p(x) = a_nx^n + a_{n-1}x^{n-1} + \hdots + a_0
\]
is a polynomial with \(a_n \neq 0\), and \(a_n, a_{n-1}, \hdots, a_0 \in C\), then \(p(x)\) factors into linear factors,
\[
p(x) = a_n \cdot (x - r_1) \cdot (x - r_2) \cdot \hdots \cdot (x - r_n).
\]
\end{theorem}
\end{document}