diff --git a/packages/libro-app/src/index.less b/packages/libro-app/src/index.less
index b418c3db..09033303 100644
--- a/packages/libro-app/src/index.less
+++ b/packages/libro-app/src/index.less
@@ -29,6 +29,7 @@
   h4,
   h5,
   h6 {
+    font-weight: bold;
     color: unset;
   }
 
diff --git a/packages/libro-core/src/index.less b/packages/libro-core/src/index.less
index 3376e307..13b68e47 100644
--- a/packages/libro-core/src/index.less
+++ b/packages/libro-core/src/index.less
@@ -23,6 +23,7 @@
   h5,
   h6 {
     color: unset;
+    font-weight: bold;
   }
 
   h1 {