add overlay as a default TiKZ option

slides_template/example.tex

@@ -18,7 +18,7 @@
 % add tikz and a bunch of tikz foo
 \usepackage{tikz}
 \usetikzlibrary{shapes,shapes.misc,backgrounds,fit,positioning}
-\tikzstyle{every picture}+=[remember picture]
+\tikzstyle{every picture}+=[overlay,remember picture]
 
 % add functions to circle parts of slides (e.g., in tables)
 \newcommand\marktopleft[1]{%
@@ -53,7 +53,6 @@
     \e{#2}
 
   }
-%  \end{center}
 }