Fix #101: set colours for Verbatim without using private Sphinx macros (

#102)

* Fix #101: set colours for Verbatim without using private Sphinx macros

The \colorlet macro is provided by xcolor package which is part of the
template anyhow (and probably loaded by some other packages from the
template).

Else, if with 'color' package and not 'xcolor' package, we could have
used \sphinxcolorlet which is avaiable since Sphinx 1.5 from December
2016.

The scope of \colorlet is limited by the environment.

This avoids using private Sphinx macro \spx@verbatimfcolorbox which got
renamed at Sphinx 5.1.0 and whose definition would thus remain without
effect.

* Remove unneeded \makeatletter/\makeatother at end of JupyterBook.cls

Co-authored-by: AakashGC <aakashguptachoudhury@gmail.com>

sphinx_jupyterbook_latex/theme/jupyterBook.cls

@@ -76,15 +76,15 @@
 {\endMakeFramed}
 
 % Env which wraps code cell inputs
-\makeatletter
 \newenvironment{sphinxVerbatimInput}
-  {\def\spx@verbatimfcolorbox{\spx@fcolorbox{CodeBlockInputBorderColor}{CodeBlockInputColor}}\begin{adjustwidth}{5pt}{}}
+  {\colorlet{VerbatimBorderColor}{CodeBlockInputBorderColor}%
+   \colorlet{VerbatimColor}{CodeBlockInputColor}%
+   \begin{adjustwidth}{5pt}{}}
   {\end{adjustwidth}}
-\makeatother
 
 % Env which wraps code cell outputs
-\makeatletter
 \newenvironment{sphinxVerbatimOutput}
-  {\def\spx@verbatimfcolorbox{\spx@fcolorbox{CodeBlockOutputBorderColor}{CodeBlockOutputColor}} \begin{adjustwidth}{20pt}{}}
+  {\colorlet{VerbatimBorderColor}{CodeBlockOutputBorderColor}%
+   \colorlet{VerbatimColor}{CodeBlockOutputColor}%
+   \begin{adjustwidth}{20pt}{}}
   {\end{adjustwidth}}
-\makeatother