feat: reinstate support for block option

Closes #6. Thanks @samcarter.

doc/moloch.tex

@@ -260,6 +260,11 @@ \subsubsection{Outer theme}
 
 \subsubsection{Color theme}
 
+\DescribeOption{block}{transparent, fill}{transparent}{
+  Optionally adds a light grey background to block environments like |theorem|
+  and |example|.
+}
+
 \DescribeOption{background}{dark, light}{light}{
   Provides the option to have a dark background and light foreground instead
   of the reverse.

examples/demo/demo.tex

@@ -150,21 +150,43 @@ \section{Elements}
     \end{tabular}
   \end{table}
 \end{frame}
-\begin{frame}{Blocks}
-  Three different block environments are pre-defined.
-
-  \begin{block}{Default}
-    Block content.
-  \end{block}
-
-  \begin{alertblock}{Alert}
-    Block content.
-  \end{alertblock}
-
-  \begin{exampleblock}{Example}
-    Block content.
-  \end{exampleblock}
-
+\begin{frame}[fragile]{Blocks}
+  Three different block environments are pre-defined: \verb|block|, \verb|alertblock|,
+  and \verb|exampleblock|. They can be styled using the option
+  \verb|block|, which takes values \verb|transparent| (default, left column) and \verb|fill| (right column).
+
+  \begin{columns}[T]
+    \begin{column}{0.45\textwidth}
+      \begin{block}{Default}
+        Block content.
+      \end{block}
+
+      \begin{alertblock}{Alert}
+        Block content.
+      \end{alertblock}
+
+      \begin{exampleblock}{Example}
+        Block content.
+      \end{exampleblock}
+    \end{column}
+    \begin{column}{0.45\textwidth}
+      {
+        \molochset{block=fill}
+
+        \begin{block}{Default}
+          Block content.
+        \end{block}
+
+        \begin{alertblock}{Alert}
+          Block content.
+        \end{alertblock}
+
+        \begin{exampleblock}{Example}
+          Block content.
+        \end{exampleblock}
+      }
+    \end{column}
+  \end{columns}
 \end{frame}
 
 \begin{frame}{Math}

src/beamercolorthememoloch.dtx

@@ -36,6 +36,18 @@
 %
 % \subsubsection{Options}
 %
+% \begin{macro}{block}
+%    Optionally adds a light grey background to block environments like
+%    |theorem| and |example|.
+%    \begin{macrocode}
+\pgfkeys{
+  /moloch/color/block/.cd,
+  .is choice,
+  transparent/.code=\moloch@block@transparent,
+  fill/.code=\moloch@block@fill,
+}
+%    \end{macrocode}
+% \end{macro}
 %
 % \begin{macro}{colors}
 %    Provides the option to have a dark background and light foreground instead
@@ -161,9 +173,37 @@
 }
 %    \end{macrocode}
 %
-% Block environments use alerted tex and example text for the title
+% Block environments such as |theorem| and |example| have no background color
+% by default. The option |block=fill| sets a background color based on the
+% background and foreground of |normal text|. The option |block=transparent|
+% reverts the block environments to an empty background, which can be useful
+% if changing colors mid-presentation.
 %
 %    \begin{macrocode}
+\newcommand{\moloch@block@transparent}{
+  \setbeamercolor{block title}{bg=}
+  \setbeamercolor{block body}{bg=}
+  \setbeamercolor{block title alerted}{bg=}
+  \setbeamercolor{block title example}{bg=}
+}
+\newcommand{\moloch@block@fill}{
+  \setbeamercolor{block title}{%
+    bg=normal text.bg!80!fg
+  }
+  \setbeamercolor{block body}{%
+    bg=block title.bg!50!normal text.bg
+  }
+  \setbeamercolor{block title alerted}{%
+    bg=block title.bg,
+  }
+  \setbeamercolor{block title example}{%
+    bg=block title.bg,
+  }
+}
+\setbeamercolor{block title}{%
+  use=normal text,
+  fg=normal text.fg
+}
 \setbeamercolor{block title alerted}{%
   use={block title, alerted text},
   fg=alerted text.fg
@@ -172,6 +212,8 @@
   use={block title, example text},
   fg=example text.fg
 }
+\setbeamercolor{block body alerted}{use=block body, parent=block body}
+\setbeamercolor{block body example}{use=block body, parent=block body}
 %    \end{macrocode}
 %
 % Footnotes
@@ -181,6 +223,14 @@
 \setbeamercolor{footnote mark}{fg=.}
 %    \end{macrocode}
 %
+%
+% Footnotes
+%
+%    \begin{macrocode}
+\setbeamercolor{footnote}{fg=normal text.fg!90}
+\setbeamercolor{footnote mark}{fg=.}
+%    \end{macrocode}
+%
 % We also reset the bibliography colors in order to pick up the surrounding
 % colors at the time of use. This prevents us having to set the correct color in
 % normal and standout mode.

testfiles/support/molochexample.tex

@@ -71,6 +71,43 @@ \subsection{Proof of the Main Theorem}
   \end{itemize}
 \end{frame}
 
+\begin{frame}{Blocks}
+  \begin{columns}
+    \begin{column}{0.45\textwidth}
+      \begin{block}{Default}
+        Block content.
+      \end{block}
+
+      \begin{alertblock}{Alert}
+        Block content.
+      \end{alertblock}
+
+      \begin{exampleblock}{Example}
+        Block content.
+      \end{exampleblock}
+    \end{column}
+    \begin{column}{0.45\textwidth}
+      {
+        \molochset{block=fill}
+
+        \begin{block}{Default}
+          Block content.
+        \end{block}
+
+        \begin{alertblock}{Alert}
+          Block content.
+        \end{alertblock}
+
+        \begin{exampleblock}{Example}
+          Block content.
+        \end{exampleblock}
+      }
+    \end{column}
+  \end{columns}
+
+
+\end{frame}
+
 \appendix
 
 \begin{frame}{Backup slides}