diff --git a/__pycache__/app.cpython-313.pyc b/__pycache__/app.cpython-313.pyc
index 6aa07ec..2e4e59d 100644
Binary files a/__pycache__/app.cpython-313.pyc and b/__pycache__/app.cpython-313.pyc differ
diff --git a/migrations/versions/add_mindmap_shares_table.py b/migrations/versions/add_mindmap_shares_table.py
new file mode 100644
index 0000000..4aa52dc
--- /dev/null
+++ b/migrations/versions/add_mindmap_shares_table.py
@@ -0,0 +1,38 @@
+"""add mindmap shares table
+
+Revision ID: add_mindmap_shares
+Revises: add_missing_user_fields
+Create Date: 2025-05-10 23:20:00.000000
+
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import sqlite
+
+# revision identifiers, used by Alembic.
+revision = 'add_mindmap_shares'
+down_revision = 'add_missing_user_fields'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # Erstelle PermissionType Enum
+    op.create_table('mindmap_share',
+        sa.Column('id', sa.Integer(), nullable=False),
+        sa.Column('mindmap_id', sa.Integer(), nullable=False),
+        sa.Column('shared_by_id', sa.Integer(), nullable=False),
+        sa.Column('shared_with_id', sa.Integer(), nullable=False),
+        sa.Column('permission_type', sa.String(20), nullable=False),
+        sa.Column('created_at', sa.DateTime(), nullable=True),
+        sa.Column('last_accessed', sa.DateTime(), nullable=True),
+        sa.ForeignKeyConstraint(['mindmap_id'], ['user_mindmap.id'], ),
+        sa.ForeignKeyConstraint(['shared_by_id'], ['user.id'], ),
+        sa.ForeignKeyConstraint(['shared_with_id'], ['user.id'], ),
+        sa.PrimaryKeyConstraint('id'),
+        sa.UniqueConstraint('mindmap_id', 'shared_with_id', name='unique_mindmap_share')
+    )
+
+
+def downgrade():
+    op.drop_table('mindmap_share')
\ No newline at end of file
diff --git a/templates/errors/400.html b/templates/errors/400.html
index 7bd28df..87ccf67 100644
--- a/templates/errors/400.html
+++ b/templates/errors/400.html
@@ -3,36 +3,46 @@
 {% block title %}400 - Ungültige Anfrage{% endblock %}
 
 {% block content %}
-<div class="min-h-[75vh] flex flex-col items-center justify-center px-4 py-12 bg-gradient-to-b from-gray-50 to-gray-100 dark:from-gray-900 dark:to-gray-800">
-    <div class="glass-effect max-w-2xl w-full p-6 md:p-10 rounded-xl border border-gray-300/20 dark:border-gray-700/30 shadow-xl transform transition-all duration-300 hover:shadow-2xl">
-        <div class="text-center">
-            <div class="flex justify-center mb-6">
-                <div class="relative">
-                    <h1 class="text-7xl md:text-8xl font-extrabold text-primary-600 dark:text-primary-400 opacity-90">400</h1>
-                    <div class="absolute -top-4 -right-4 w-12 h-12 bg-red-500 rounded-full flex items-center justify-center animate-pulse">
-                        <i class="fa-solid fa-exclamation text-white text-xl"></i>
+<div class="container mx-auto max-w-4xl px-4 py-8">
+    <div class="bg-white dark:bg-gray-800 rounded-lg shadow-xl p-8 border border-gray-200 dark:border-gray-700">
+        <div class="text-center mb-8">
+            <div class="text-6xl font-bold text-red-500 mb-4">400</div>
+            <h1 class="text-3xl font-bold mb-2">Ungültige Anfrage</h1>
+            <p class="text-gray-600 dark:text-gray-400">Die Anfrage konnte nicht verarbeitet werden.</p>
+        </div>
+
+        <div class="mb-8 p-4 border border-red-200 dark:border-red-900 bg-red-50 dark:bg-red-900/20 rounded-lg">
+            <div class="flex items-start">
+                <div class="flex-shrink-0">
+                    <svg class="h-5 w-5 text-red-500" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 20" fill="currentColor">
+                        <path fill-rule="evenodd" d="M10 18a8 8 0 100-16 8 8 0 000 16zM8.707 7.293a1 1 0 00-1.414 1.414L8.586 10l-1.293 1.293a1 1 0 101.414 1.414L10 11.414l1.293 1.293a1 1 0 001.414-1.414L11.414 10l1.293-1.293a1 1 0 00-1.414-1.414L10 8.586 8.707 7.293z" clip-rule="evenodd" />
+                    </svg>
+                </div>
+                <div class="ml-3">
+                    <h3 class="text-sm font-medium text-red-800 dark:text-red-400">Fehlerbeschreibung</h3>
+                    <div class="mt-2 text-sm text-red-700 dark:text-red-300">
+                        {% if error %}
+                        <p>{{ error }}</p>
+                        {% else %}
+                        <p>Die Anfrage enthält ungültige oder fehlerhafte Daten und konnte nicht verarbeitet werden.</p>
+                        {% endif %}
                     </div>
                 </div>
             </div>
-            <h2 class="text-2xl md:text-3xl font-semibold mb-4 text-gray-800 dark:text-gray-200">Ungültige Anfrage</h2>
-            <p class="text-gray-600 dark:text-gray-300 mb-8 max-w-lg mx-auto text-base md:text-lg">Die Anfrage konnte nicht verarbeitet werden. Bitte überprüfen Sie Ihre Eingaben und versuchen Sie es erneut.</p>
-            {% if error %}
-            <div class="mb-6 p-4 bg-red-100 dark:bg-red-900/30 text-red-800 dark:text-red-200 rounded-lg text-sm">
-                {{ error }}
-            </div>
-            {% endif %}
-            <div class="flex flex-col sm:flex-row gap-4 justify-center">
-                <a href="{{ url_for('index') }}" class="btn-primary transform transition-transform duration-300 hover:scale-105 px-6 py-3 rounded-lg">
-                    <i class="fa-solid fa-home mr-2"></i>Zur Startseite
-                </a>
-                <a href="javascript:history.back()" class="btn-secondary transform transition-transform duration-300 hover:scale-105 px-6 py-3 rounded-lg">
-                    <i class="fa-solid fa-arrow-left mr-2"></i>Zurück
-                </a>
-            </div>
         </div>
-    </div>
-    <div class="mt-8 text-sm text-gray-500 dark:text-gray-400">
-        <p>Benötigen Sie Hilfe? <a href="#" class="text-primary-600 dark:text-primary-400 hover:underline">Kontaktieren Sie uns</a></p>
+
+        <div class="text-center">
+            <p class="mb-4 text-gray-600 dark:text-gray-400">Hier sind einige Dinge, die Sie versuchen können:</p>
+            <ul class="list-disc list-inside text-left max-w-md mx-auto mb-6 text-gray-600 dark:text-gray-400">
+                <li>Überprüfen Sie Ihre Eingaben auf Fehler.</li>
+                <li>Stellen Sie sicher, dass Sie die richtigen Daten übermittelt haben.</li>
+                <li>Versuchen Sie, die Seite neu zu laden.</li>
+                <li>Kehren Sie zur Startseite zurück und versuchen Sie es erneut.</li>
+            </ul>
+            <a href="{{ url_for('index') }}" class="inline-flex items-center px-4 py-2 border border-transparent text-sm font-medium rounded-md shadow-sm text-white bg-blue-600 hover:bg-blue-700 focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-blue-500">
+                Zurück zur Startseite
+            </a>
+        </div>
     </div>
 </div>
 {% endblock %}
\ No newline at end of file