\usepackage{titlesec}
\usepackage[many]{tcolorbox}
\usepackage{environ}

\titlespacing*{\chapter}{0cm}{-2.0cm}{0.50cm}
\titlespacing*{\section}{0cm}{0.50cm}{0.25cm}

\setlength{\parindent}{0pt}
\setlength{\parskip}{1ex}

\newtcbtheorem[list inside={prob}]{problem}{Problema}%
    {enhanced,
    colback = black!5, %white,
    colbacktitle = black!5,
    coltitle = black,
    boxrule = 0pt,
    frame hidden,
    borderline west = {0.5mm}{0.0mm}{black},
    fonttitle = \bfseries\sffamily,
    breakable,
    before skip = 3ex,
    after skip = 3ex,
    boxsep = 2mm
}{problem}

\newenvironment{solution}
  {\let\qed\relax\begin{proof}[Soluzione]}
  {\end{proof}}

\newenvironment{altsolution}
  {\let\qed\relax\begin{proof}[Soluzione alternativa]}
  {\end{proof}}

\newif\ifhideproofs
% \hideproofstrue

\ifhideproofs
  \usepackage{environ}
  \NewEnviron{hide}{}
  \let\solution\hide
  \let\endsolution\endhide
  \let\altsolution\hide
  \let\endaltsolution\endhide
\fi

\tcbuselibrary{skins, breakable}