Boxes Placement In Tcolorbox

Answer :

Obviously, you would use the \tcbox macro version for your boxes, rather than the environment form. Calculation of the stackgap is shown automated in this MWE. (Note: this example works starting with V2.30 of tcolorbox).

\documentclass{article} \usepackage{stackengine} \usepackage{tcolorbox} \begin{document}  \def\boxone{\tcbox[nobeforeafter]{This is a test}} \def\boxtwo{\tcbox[nobeforeafter]{Another test}} \def\boxthree{\tcbox[nobeforeafter,minipage,width=0.7in]{this is a very long box}}  \stackon[\heightof{\boxthree}-\heightof{\boxone}-\heightof{\boxtwo}]%   {\boxtwo}{\boxone}~\boxthree  \end{document} 

Taking a similar tack to Steven Segletes's answer but using the xcoffins package, which allows us to pick points on the various boxes to line up:

\documentclass{article} \usepackage{tcolorbox}  \usepackage{xcoffins} \NewCoffin{\CoffinA} \NewCoffin{\CoffinB} \NewCoffin{\CoffinC} \begin{document} % Set up content in three coffins \SetHorizontalCoffin{\CoffinA}{%   \begin{tcolorbox}[width = 1 in]     This is a \textbf{tcolorbox}.%   \end{tcolorbox} }% \SetHorizontalCoffin{\CoffinB}{%   \begin{tcolorbox}[width = 1 in]     This is a \textbf{tcolorbox}.%   \end{tcolorbox} }% \SetHorizontalCoffin{\CoffinC}{\rule{1 in}{2.5 in}}% % Join the first small coffin onto the big one at the top \JoinCoffins{\CoffinC}[t,l]{\CoffinA}[t,r](-0.1 in, 0 in)% % Join the second small coffin onto the big one at the bottom \JoinCoffins{\CoffinC}[b,\CoffinC-l]{\CoffinB}[b,r](-0.1 in, 0 in)% \TypesetCoffin{\CoffinC}  \end{document} 

Here, I've added a small gap between the coffins (it's negative as I've done everything relative to the large item, \CoffinC.)

The 'coffin' system works by having 'handles' on the boxes it creates: we can address those by letters, e.g. t for 'top', and also refer to points on coffins we've already combined. This allows relatively easy construction of complex box relationships.