tcolorbox spacing with \center environment and \centering switch

Question

In LaTeX, the way \begin{center}....\end{center} spaces the tcolorbox is different from how \centering does it. The center environment, provides enough space but the vertical spacing done with \centering isn't the same as with center environment. Now my question is, when using \centering, how do I achieve the same spacing of tcolorbox as done with center environment.

Here is the MWE:

\documentclass[12pt]{article}
\usepackage[many]{tcolorbox}
\usepackage{kantlipsum}

\newcommand{\unittcbox}[1]{%
\medskip \centering \tcbox{#1} \medskip
}%
\begin{document}
\kant[1]
\unittcbox{SI unit :  Ampere. square metre ($A.m²$)}
\kant[2]
\begin{center}
\tcbox{SI unit :  Ampere. square metre ($A.m²$)}
\end{center}
\kant[3]
\end{document}

I tried with \medskip but it didn't workout.

Using centering:

Using center environment:

Answer 1

May be this is what you want.

\documentclass[12pt]{article}
\usepackage[many]{tcolorbox}
\usepackage{siunitx}
\usepackage{kantlipsum}
\newtcolorbox{units}{before=\par\smallskip\centering,after=\par,hbox}

\begin{document}
\kant*[2]
\begin{units}
SI unit :  Ampere. square metre (\si{A.m^2})
\end{units}
Some text comes here just for demo.
\kant[3]
\end{document}

I have defined a new environment so that you don't have to type much every time.

If you want more space, you may use

\newtcolorbox{units}{before=\begin{center},after=\end{center},hbox}

or manually adjust the space as in

\newtcolorbox{units}{before=\par\bigskip\centering,after=\par\bigskip,hbox}

Answer 2

My impression is that you want to use the on line option:

\documentclass[12pt]{article}
\usepackage[many]{tcolorbox}
\usepackage{siunitx}
\usepackage{kantlipsum}

\begin{document}
\kant*[2]
\begin{center}
\tcbox[on line]{SI unit :  Ampere. square metre (\si{A.m^2})}
\end{center}
\kant[3]
\end{document}