diff --git a/src/theme/book.css b/src/theme/book.css
index e2f03e65..386cb28f 100644
--- a/src/theme/book.css
+++ b/src/theme/book.css
@@ -5,6 +5,7 @@ body {
 }
 body {
   margin: 0;
+  font-size: 1rem;
 }
 code {
   font-family: "Source Code Pro", Consolas, "Ubuntu Mono", Menlo, "DejaVu Sans Mono", monospace, monospace;
diff --git a/src/theme/stylus/general.styl b/src/theme/stylus/general.styl
index 210c3788..9a5cc974 100644
--- a/src/theme/stylus/general.styl
+++ b/src/theme/stylus/general.styl
@@ -5,6 +5,7 @@ html, body {
 
 body {
     margin: 0;
+    font-size: 1rem;
 }
 
 code {