diff --git a/book/tables/vars.tex b/book/tables/vars.tex
index e9764c8..38c8823 100644
--- a/book/tables/vars.tex
+++ b/book/tables/vars.tex
@@ -1,2 +1,4 @@
 \documentclass{standalone}
 \usepackage{booktabs}
+\usepackage{makecell}
+\renewcommand\theadfont{\bfseries}