diff --git a/src/themes/buble.styl b/src/themes/buble.styl
index 71c97e573..2b0711959 100644
--- a/src/themes/buble.styl
+++ b/src/themes/buble.styl
@@ -112,6 +112,7 @@ $sidebar-width = 16rem
   padding 0 10px 12px 0
   overflow auto
   word-wrap normal
+  position relative
 
 /* code highlight */
 .token.cdata, .token.comment, .token.doctype, .token.prolog