# tcolorbox: Also make rules transparent

I would like to completely hide the contents of tcolorboxes (on non-white, non-uniform background), even all rules in equations. The latter are the only remaining things when one sets opacitytext=0.

\documentclass{scrartcl}
\usepackage[most]{tcolorbox}
\usepackage{amsmath}

\begin{document}
\begin{tcolorbox}[enhanced, opacitytext=0]
\begin{align}
\frac{a}{b}=\underline{c}
\end{align}
\end{tcolorbox}
\end{document}


Is there a way to also hide the remaining lines?

Use the option tikz={opacity=0} in addition to opacitytext=0 in order to hide anything inside the box, since the enhanced skin style uses tikzpicture as the drawing 'machine' -- the option tikz={opacity=0} is handed over to tikzpicture and drawing is 'silenced'.

The first box shows the hidden content, the second one is the box without using tikz={opacity=0} as done by the O.P.

\documentclass{article}
\usepackage{amsmath}
\usepackage[most]{tcolorbox}

\begin{document}
\begin{tcolorbox}[enhanced,opacitytext=0.0,tikz={opacity=0}]
\begin{align}
\frac{a}{b}=\underline{c}
\end{align}
\end{tcolorbox}

\begin{tcolorbox}[enhanced,opacitytext=0.0]
\begin{align}
\frac{a}{b}=\underline{c}
\end{align}
\end{tcolorbox}

\end{document}


I don't really get what you really need (might be an X-Y problem), but the following code hides the complete contents of your colorbox:

\documentclass{scrartcl}
\usepackage[most]{tcolorbox}
\usepackage{amsmath}

\begin{document}
\begin{tcolorbox}[enhanced] %now optional: opacitytext=0
\phantom{%
\begin{minipage}{\columnwidth}%
\begin{align}
\frac{a}{b}=\underline{c}
\end{align}
\end{minipage}%
}%
\end{tcolorbox}
\end{document}


Explanation:

• \phantom occupies the space of its contents, but does not display it
• minipage makes it possible to use align in the \phantom
• The disadvantage of this solution is that one has to use \phantom each time explicitly for all boxes for which the content should be hidden. – user31729 Sep 28 '17 at 14:09