[Tex/LaTex] Indent in itemize/enumerate with different width for body and for item

Question

I'm having some troubles with the customisation of the indent of itemize environment. My MWE is:

\documentclass{article}
    \usepackage{lipsum}
    \usepackage[utf8]{inputenc}
    \usepackage{enumitem}

\begin{document}%

\lipsum[1-2]

\begin{itemize}[leftmargin=3cm]
    \item [My custom item long long long long]: \lipsum[1]
    \item [My custom item short]: \lipsum[2]
\end{itemize}

\end{document}%

The output:

Now, i would like to have the two custom labels at the same width, and not one more indented of another. Plus I would like to decide where the text of the item stars (in this case, due to the [leftmargin=3cm] option is too much indented, otherwise the two labels wouldn't have been inside the page).

How can I deal with margins, alignment and indentation od itemize/enumerate?
Thanks for help!

P.S.: The next image will eventually clarify what I would like to have

Answer 1

Maybe like this, with a custom description environment?

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{enumitem}
\usepackage{lipsum}

\begin{document}%

\lipsum[1-2]
\begin{description}[leftmargin=1cm, labelindent=-3cm, labelsep=0pt, font=\normalfont]
    \item[ My custom item long long long long]: \lipsum[1]
    \item [My custom item short]: \lipsum[2]
\end{description}

\end{document}