diff --git a/style.css b/style.css
new file mode 100644
index 0000000..a843549
--- /dev/null
+++ b/style.css
@@ -0,0 +1,46 @@
+/* Light mode (default) */
+body {
+  margin: 0;
+  font-family: Arial, sans-serif;
+  background: #f4f4f4;
+  color: #111;
+  transition: background 0.3s, color 0.3s;
+}
+
+.container {
+  max-width: 600px;
+  margin: 100px auto;
+  text-align: center;
+  padding: 40px;
+  background: white;
+  border-radius: 12px;
+  box-shadow: 0 0 20px rgba(0,0,0,0.1);
+  transition: background 0.3s;
+}
+
+button {
+  margin-top: 20px;
+  padding: 12px 20px;
+  font-size: 16px;
+  border: none;
+  border-radius: 8px;
+  cursor: pointer;
+  background: #222;
+  color: white;
+}
+
+/* Dark mode */
+body.dark {
+  background: #121212;
+  color: #f1f1f1;
+}
+
+body.dark .container {
+  background: #1e1e1e;
+  box-shadow: 0 0 20px rgba(255,255,255,0.05);
+}
+
+body.dark button {
+  background: white;
+  color: black;
+}