diff --git a/slides.pdf b/slides.pdf
index 94dc9faa18e9375f390b9106492d510f42bc1e9b..dbcb31669971af30459497a6c5ac2cfd0e7491df 100644
Binary files a/slides.pdf and b/slides.pdf differ
diff --git a/slides.tex b/slides.tex
index f018ec769d6f3aa4926c3659a2aeef6a97806f38..0e6a9b31f3a01dfa2c1fd54b72ed64ef6dc764c0 100644
--- a/slides.tex
+++ b/slides.tex
@@ -405,11 +405,11 @@ Nix uses a single directory to store every packages.
 
   \only<1>{
     \vspace{1em}
-    It contains the derivations of all application (and libraries) \emph{officialy} available with Nix.
+    It contains the derivations of all application (and libraries) \emph{officialy} available with Nix. \\
   }
   \only<1>{
     \vspace{1em}
-    Packages are distributed as Nix expression (the so called derivations).
+    In short, \textbf{packages are declared as source code}.
   }
 
 \end{frame}
@@ -417,11 +417,14 @@ Nix uses a single directory to store every packages.
 \begin{frame}[plain]{Channels}
 
   \only<1>{
-  \textbf{NixPkgs} is a git repository containing the code of all \emph{official} derivations.
 
   \vspace{1em}
-
+\begin{tcolorbox}[colframe=black,colback=gray!10,coltext=black]
+  \center
   A \textbf{channel} is link to  branch of NixPkgs tested with continuous integration.
+\end{tcolorbox}
+
+
 
   \vspace{1em}
 
@@ -434,8 +437,10 @@ Nix uses a single directory to store every packages.
 
   \only<2>{
 
+\begin{tcolorbox}[colframe=red!17,colback=red!10,coltext=black]
+  \center
     Channels are not fully reproducible, as they are subject to updates.
-
+\end{tcolorbox}
   }
 
 \end{frame}
@@ -524,7 +529,7 @@ Nix uses a single directory to store every packages.
     \includegraphics[scale=0.035]{figures/UncheckedBox} &  
     \includegraphics[scale=0.035]{figures/CheckedBox}\\ 
     \hline
-  \end{tabular} 
+  \end{tabular}
 \end{frame}