Prevent form tags from removing custom class attrs

hshassets/templatetags/bulma.py

@@ -20,7 +20,9 @@ def bulma_form_fields(form):
         if field.errors:
             widget_classes.append("is-danger")
         # done
-        field.field.widget.attrs["class"] = " ".join(widget_classes)
+        if field.field.widget.attrs.get('class'):
+            widget_classes.append(field.field.widget.attrs['class'])
+        field.field.widget.attrs['class'] = " ".join(widget_classes)
     if getattr(form, 'layout', None):
         output = render_layout(form.layout, form)
     else: