general error view

app/routes.py

 import uuid
 import os
 from datetime import datetime, timedelta
+from werkzeug.exceptions import HTTPException
 from werkzeug.utils import secure_filename
 from app import app, db
 from flask import redirect, url_for, render_template, send_from_directory, current_app, abort
@@ -68,6 +69,11 @@ def index():
     return redirect(url_for('upload'))
 
 
+@app.errorhandler(HTTPException)
+def http_error(e):
+    return render_template('Error.html', e=e)
+
+
 @app.route('/expired')
 @app.errorhandler(404)
 def expired(e=None):

app/templates/Error.html

+{% extends 'BasePage.html' %}
+
+{% block content %}
+    <div class="pricing-header px-3 py-3 pt-md-5 pb-md-4 mx-auto text-center">
+        <h1 class="display-4">Fehler {{ e.code }} - {{ e.name }}</h1>
+        <p class="lead">Es tut uns leid, aber es ist etwas schief gelaufen.</p>
+        <small class="d-block mb-3 text-muted">{{ e.description }}</small>
+    </div>
+{% endblock content %}