diff --git a/public/sample/html/external-css.html b/public/sample/html/external-css.html
new file mode 100644
index 0000000..7d8fdd7
--- /dev/null
+++ b/public/sample/html/external-css.html
@@ -0,0 +1,2 @@
+<link rel="stylesheet" href="./styles.css">
+<div id="button">ボタン</div>
diff --git a/public/sample/html/styles.css b/public/sample/html/styles.css
new file mode 100644
index 0000000..2e32f4a
--- /dev/null
+++ b/public/sample/html/styles.css
@@ -0,0 +1,13 @@
+#button {
+  background-color: #4CAF50;
+  /* Green */
+  border: none;
+  color: white;
+  padding: 15px 32px;
+  text-align: center;
+  text-decoration: none;
+  display: inline-block;
+  font-size: 16px;
+  margin: 4px 2px;
+  cursor: pointer;
+}