Define tcolorbox in math mode

Question

Since in my document I have to write a lot of math in colored box, I'd like to avoid to write $ inside every box. Is there a way to define newtcbox in math mode?

I tried with \newtcbox{\mywbox}[1]{<options>}{$\displaystyle #1$} but it doesn't work.

This is my latex code:

\usepackage{tcolorbox}
\newtcbox{\mywbox}{on line,colback=white,colframe=black,size=fbox,arc=3pt,boxrule=0.8pt}

\begin{document}
\obeylines

This \mywbox{$3x$} is in line math.
This $$y=\mywbox{$-5x$}-5+6$$ is not in line math.

\end{document}

I read about \tcboxmath and \tcbhighmath in the official tcolorbox manual, but I don't understand how to define them simply as the newtcbox and if they are what I need.

Answer 1

You can do this using \tcboxmath from the theorems library of tcolorbox:

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{theorems}
\newcommand*{\mywbox}{%
  \tcboxmath[colback=white, colframe=black, size=fbox, arc=3pt, boxrule=0.8pt]%
}
\begin{document}
This \mywbox{3x} is in line math.
This
[ y = \mywbox{-5x} - 5 + 6 ]
is not in line math.
\end{document}

You may want to abstract things a little bit using a style too, so that you can apply it to other boxes should the need arise:

\documentclass{article}
\usepackage{tcolorbox}
\tcbuselibrary{theorems}
\tcbset{my math box/.style={
          colback=white, colframe=black, size=fbox, arc=3pt, boxrule=0.8pt}
}
\newcommand*{\mywbox}{\tcboxmath[my math box]}
\begin{document}
This \mywbox{3x} is in line math.
This
[ y = \mywbox{-5x} - 5 + 6 ]
is not in line math.
\end{document}

Making the background of the box transparent

This can be done using /tcb/opacityback and a skin using a jigsaw frame engine, such as standard jigsaw or enhanced jigsaw.

\documentclass[fleqn]{article}
\usepackage{tcolorbox}
\tcbuselibrary{theorems}
\tcbset{
  my math box/.style={
    standard jigsaw,   % useful for 'opacityback' and 'opacityframe'
    colback=green!20, colframe=black, size=fbox, arc=3pt, boxrule=0.8pt,
    opacityback=0.6,
  }
}
\newcommand*{\mywbox}{\tcboxmath[my math box]}
\begin{document}
This \makebox[0pt]{%
  \raisebox{-0.5\height}[0pt][0pt]{\hspace{1cm}\includegraphics{example-image-duck}}%
  }%
\mywbox{3x} is in line math.
This
[ y = \mywbox{-5x} - 5 + 6 ]
is not in line math.
\end{document}

Answer 2

I would say

\newtcbox{\mywboxtext}{on line,colback=white,colframe=black,size=fbox,arc=3pt,boxrule=0.8pt}
\newcommand{\mywboxmath}[1]{\mywboxtext{$#1$}}

Your example can become

\documentclass{article}
\usepackage{tcolorbox}

\newtcbox{\mywboxtext}{on line,colback=white,colframe=black,size=fbox,arc=3pt,boxrule=0.8pt}
\newcommand{\mywboxmath}[1]{\mywboxtext{$#1$}}

\begin{document}

This \mywboxmath{3x} is in line math and this
\[
y=\mywboxmath{-5x}-5+6
\]
is display math.

\end{document}

Change the names to your liking.

Avoid $$ in LaTeX (and of course also \obeylines).

Should you need the boxes to behave in subscripts or superscripts, change the code into

\documentclass{article}
\usepackage{tcolorbox}

\newtcbox{\mywboxtext}{on line,colback=white,colframe=black,size=fbox,arc=3pt,boxrule=0.8pt}

\makeatletter
\newcommand{\mywboxmath}[1]{\mathpalette\mywboxmath@do{#1}}
\newcommand{\mywboxmath@do}[2]{\mywboxtext{$\m@th#1#2$}}
\makeatother

\begin{document}

This $\mywboxmath{3x}$ is in line math and this
\[
y_{\mywboxmath{0}}=\mywboxmath{-5x}-5+6
\]
is display math.

\end{document}

Note that in this case you need that \mywboxmath is in math mode.