diff --git a/public/css/app.css b/public/css/app.css
new file mode 100644
index 0000000..2054426
--- /dev/null
+++ b/public/css/app.css
@@ -0,0 +1,137 @@
+* {
+    box-sizing: border-box;
+}
+
+body {
+    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
+    line-height: 1.6;
+    color: #222;
+    background: #fafafa;
+    margin: 0;
+    padding: 0;
+}
+
+.page {
+    max-width: 600px;
+    margin: 0 auto;
+    padding: 2rem;
+}
+
+.page-center {
+    text-align: center;
+}
+
+h1 {
+    font-size: 2.5rem;
+    margin-bottom: 1rem;
+    color: #444;
+}
+
+.page-center h1 {
+    margin-bottom: 0.5rem;
+}
+
+p {
+    font-size: 1.1rem;
+    color: #666;
+}
+
+.form-group {
+    margin-bottom: 1.5rem;
+}
+
+label {
+    display: block;
+    margin-bottom: 0.5rem;
+    color: #444;
+    font-weight: 500;
+}
+
+input[type="url"] {
+    width: 100%;
+    padding: 0.75rem;
+    font-size: 1rem;
+    border: 1px solid #ddd;
+    border-radius: 4px;
+}
+
+input[type="url"]:focus {
+    outline: none;
+    border-color: #444;
+}
+
+button {
+    width: 100%;
+    padding: 0.75rem;
+    font-size: 1rem;
+    background-color: #444;
+    color: white;
+    border: none;
+    border-radius: 4px;
+    cursor: pointer;
+    font-weight: 500;
+}
+
+button:hover {
+    background-color: #333;
+}
+
+button:disabled {
+    background-color: #999;
+    cursor: not-allowed;
+}
+
+.result {
+    margin-top: 2rem;
+    padding: 1rem;
+    border-radius: 4px;
+    display: none;
+}
+
+.result.success {
+    background-color: #e8f5e9;
+    border: 1px solid #4caf50;
+    color: #2e7d32;
+}
+
+.result.error {
+    background-color: #ffebee;
+    border: 1px solid #f44336;
+    color: #c62828;
+}
+
+.result.show {
+    display: block;
+}
+
+.short-url {
+    word-break: break-all;
+    font-weight: 500;
+    margin-top: 0.5rem;
+}
+
+.short-url a {
+    color: #2e7d32;
+    text-decoration: none;
+}
+
+.short-url a:hover {
+    text-decoration: underline;
+}
+
+.error-message {
+    margin-top: 0.5rem;
+}
+
+.link-home {
+    display: inline-block;
+    margin-top: 1.5rem;
+    color: #444;
+    text-decoration: none;
+    border-bottom: 1px solid #444;
+}
+
+.link-home:hover {
+    color: #333;
+    border-color: #333;
+}