diff --git a/src/guide/essentials/class-and-style.md b/src/guide/essentials/class-and-style.md
index b8578ad1f..b91ed29f0 100644
--- a/src/guide/essentials/class-and-style.md
+++ b/src/guide/essentials/class-and-style.md
@@ -296,7 +296,7 @@ CSS プロパティのキーにはキャメルケース（camelCase）が推奨
 ```js
 const styleObject = reactive({
   color: 'red',
-  fontSize: '13px'
+  fontSize: '30px'
 })
 ```