diff --git a/docs/1-trial-session/12-css/_samples/yellow-hello-css/index.html b/docs/1-trial-session/12-css/_samples/yellow-hello-css/index.html
index bda90e4a7..8e1d36789 100644
--- a/docs/1-trial-session/12-css/_samples/yellow-hello-css/index.html
+++ b/docs/1-trial-session/12-css/_samples/yellow-hello-css/index.html
@@ -6,6 +6,6 @@
     <title>Title</title>
   </head>
   <body>
-    <div id="div">Hello CSS!</div>
+    <div id="greeting">Hello CSS!</div>
   </body>
 </html>
diff --git a/docs/1-trial-session/12-css/_samples/yellow-hello-css/style.css b/docs/1-trial-session/12-css/_samples/yellow-hello-css/style.css
index 9ec8d3b34..5b2a2d9b6 100644
--- a/docs/1-trial-session/12-css/_samples/yellow-hello-css/style.css
+++ b/docs/1-trial-session/12-css/_samples/yellow-hello-css/style.css
@@ -1,4 +1,4 @@
-#div {
+#greeting {
   color: yellow;
   background-color: black;
 }
diff --git a/docs/1-trial-session/12-css/index.md b/docs/1-trial-session/12-css/index.md
index e362fb3b4..fd2b2e472 100644
--- a/docs/1-trial-session/12-css/index.md
+++ b/docs/1-trial-session/12-css/index.md
@@ -180,13 +180,13 @@ CSS の<Term type="cssProperty">プロパティ</Term>には `color` (文字色)
     <title>Title</title>
   </head>
   <body>
-    <div id="div">Hello CSS!</div>
+    <div id="greeting">Hello CSS!</div>
   </body>
 </html>
 ```
 
 ```css title="style.css"
-#div {
+#greeting {
   color: yellow;
   background-color: black;
 }
