improve the qrcode rendering with a bit of tikz

slides.tex

@@ -90,10 +90,10 @@
 {\setlcsbbackground{black}\lcsbwhitelogostrue
 \begin{frame}
 \centering
-\color{white}
-\qrcode[height=0.7\paperheight]{https://lcsb.uni.lu}
-
+\tikz\node[align=center,text width=.4\paperwidth,fill=white,rounded corners=1em, inner sep=1em]{
+\qrcode[height=\linewidth]{https://lcsb.uni.lu}\par
 \tiny\tt lcsb.uni.lu
+};
 \end{frame}
 }%the background change doesn't propagate outside of {braces}