diff --git a/app/templates/base.html b/app/templates/base.html
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index 0000000..27dad78
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+++ b/app/templates/base.html
@@ -0,0 +1,58 @@
+<!DOCTYPE html>
+<html lang="de">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>LeoCRM</title>
+    <style>
+        * { box-sizing: border-box; margin: 0; padding: 0; }
+        body { font-family: Arial, sans-serif; background: #f5f5f5; color: #333; }
+        nav { background: #2c3e50; color: white; padding: 1rem; display: flex; justify-content: space-between; align-items: center; }
+        nav a { color: white; text-decoration: none; margin-left: 1rem; }
+        nav a:hover { text-decoration: underline; }
+        .container { max-width: 900px; margin: 2rem auto; padding: 0 1rem; }
+        .flash { padding: 0.75rem; margin-bottom: 1rem; border-radius: 4px; }
+        .flash.success { background: #d4edda; color: #155724; border: 1px solid #c3e6cb; }
+        .flash.danger { background: #f8d7da; color: #721c24; border: 1px solid #f5c6cb; }
+        .flash.warning { background: #fff3cd; color: #856404; border: 1px solid #ffeeba; }
+        .flash.info { background: #d1ecf1; color: #0c5460; border: 1px solid #bee5eb; }
+        table { width: 100%; border-collapse: collapse; margin-top: 1rem; }
+        th, td { padding: 0.5rem; text-align: left; border-bottom: 1px solid #ddd; }
+        th { background: #f8f9fa; }
+        .btn { display: inline-block; padding: 0.4rem 0.8rem; border: none; border-radius: 4px; cursor: pointer; text-decoration: none; font-size: 0.9rem; }
+        .btn-primary { background: #007bff; color: white; }
+        .btn-danger { background: #dc3545; color: white; }
+        .btn-secondary { background: #6c757d; color: white; }
+        .btn-sm { padding: 0.2rem 0.5rem; font-size: 0.8rem; }
+        form label { display: block; margin-top: 0.5rem; font-weight: bold; }
+        form input, form textarea { width: 100%; padding: 0.4rem; margin-top: 0.2rem; border: 1px solid #ccc; border-radius: 4px; }
+        form textarea { resize: vertical; min-height: 60px; }
+        form button { margin-top: 1rem; }
+    </style>
+</head>
+<body>
+    <nav>
+        <span><strong>LeoCRM</strong></span>
+        <span>
+            {% if session.username %}
+                <span>{{ session.username }}</span>
+                <a href="{{ url_for('dashboard') }}">Dashboard</a>
+                <a href="{{ url_for('logout') }}">Logout</a>
+            {% else %}
+                <a href="{{ url_for('login') }}">Login</a>
+                <a href="{{ url_for('register') }}">Register</a>
+            {% endif %}
+        </span>
+    </nav>
+    <div class="container">
+        {% with messages = get_flashed_messages(with_categories=true) %}
+            {% if messages %}
+                {% for category, message in messages %}
+                    <div class="flash {{ category }}">{{ message }}</div>
+                {% endfor %}
+            {% endif %}
+        {% endwith %}
+        {% block content %}{% endblock %}
+    </div>
+</body>
+</html>
