diff --git a/category-theory.sty b/category-theory.sty
index 63c5557..6ccefde 100644
--- a/category-theory.sty
+++ b/category-theory.sty
@@ -13,3 +13,12 @@
 
 \newcommand{\gkl}[1]{\left\{ #1 \right\}}
 \newcommand{\kl}[1]{\left( #1 \right) }
+
+\usepackage[skins]{tcolorbox}
+
+\newtcolorbox{recap}{before skip = 0.5cm, after skip = 0.5cm, enhanced, sharp corners = all, colback = white, colframe = gray, toprule=0pt, bottomrule=0pt, leftrule=0pt,rightrule=0pt, overlay = {
+        \draw[gray, line width = 2pt] (frame.north west) -- ++(0.5cm, 0pt);
+        \draw[gray, line width=2pt] (frame.south east) -- ++(-0.5cm, 0pt);
+        \draw[gray, line width=2pt] (frame.north west) -- ++ (0pt, -0.5cm);
+        \draw[gray, line width=2pt] (frame.south east) -- ++(0pt, 0.5cm);
+}}