✨ Allow custom styles system wide

Should fix #4060

src/Wallabag/CoreBundle/Resources/views/base.html.twig

@@ -43,6 +43,7 @@
 
             {% block css %}
             {% endblock %}
+            <link rel="stylesheet" href="{{ asset('custom.css') }}">
             {% block scripts %}
             <script src="{{ asset('bundles/fosjsrouting/js/router.js') }}"></script>
             <script src="{{ path('fos_js_routing_js', { callback: 'fos.Router.setData' }) }}"></script>